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AND  METALLURGY, 
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MATERIALS  OF   CONSTRUCTION. 

A  Text-book  for  Technical  Schools,  condensed  from  Thurston's  "  Materials  of  Engi- 
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Containing  an  explanation  of  th3  Theory  of  Friction,  and  an  account  of  the  various 
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STEAM   BOILER    EXPLOSIONS   IN   THEORY   AND   IN  PRACTICE. 

Containing  Causes  of — Preventives — Emergencies — Low  Water — Consequences — 
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A   MANUAL 


OF 


STEAM-BOILERS 


THEIR 


DESIGN,  CONSTRUCTION,  AND  OPERATION. 


FOR     TECHNICAL    SCHOOLS    AND    ENGINEERS. 


BY 


R.  H.  ^HUsTOtf,  M.A:,cDoc.  ENG.; 

Director  of  Sibley  College,  Ojrnejl  Univtrsity^  ?a$t\  grtsident  American  Society 

of  Mechanical  Engineers  ;  Author  of  a  "  History  of  the  Steam-engine," 

'  '  Materials  of  Engineering"  etc.  ,  etc.  ,  etc. 


NEW  YORK: 
JOHN    WILEY    &    SONS, 

15   ASTOR   PLACE. 
1888. 


/  6^ 


Copyright,  1888, 
By  R.  H.  THURSTON. 


GIFT  OF 


ENGINEERING  LIBRARY 


DRUMMOND  &  NEU, 

Electrotypers, 

1  to  7  Hague  Street. 

New  York. 


PREFACE. 


THE  following  treatise  on  the  steam  boiler,  its  design,  con- 
struction, and  operation,  is  the  outcome  of  an  attempt  to  meet 
a  demand  which  has  been  repeatedly  made  for  a  fairly  com- 
plete, systematic,  and  scientific,  yet  "  practical,"  manual.  It 
has  been  intended  to  work  to  a  plan  that  should  be  sufficiently 
comprehensive  to  meet  the  wants  of  the  engineer  in  his  office, 
and  yet  so  rigidly  systematic  as  to  be  suitable  for  use  as  a 
text-book  in  schools  of  engineering.  It  has  been  the  endeavor 
to  incorporate  the  elements  of  the  subject  just  so  far  as  they 
are  needed  in  preparing  the  way  for  the  work  of  the  designer, 
the  builder,  and  the  manager  of  steam-boilers ;  while  also 
amply  complete  and  logical  to  permit  the  use  of  the  book  in 
the  instruction  of  the  student  in  applied  science.  It  was  not 
expected  that  it  would  be  found  practicable  to  make  a  manual 
of  this  kind  absolutely  complete  as  a  workshop  treatise  to  be 
used  by  the  boiler-maker — a  trade  manual ;  but  it  was  hoped 
that  it  might,  within  these  limits,  be  made  fairly  satisfactory  to 
the  engineer  engaged  in  designing. 

The  plan  of  the  work  is  as  follows:  Beginning  with  an  his- 
torical and  descriptive  introduction,  in  which  are  traced  the 
various  developments  of  the  apparatus  used  by  the  engineers  of 
the  time  of  Watt  and  earlier,  and  by  his  successors,  and  the 
progress  made  since  his  time  to  date,  the  existing  standard 
forms  of  boiler  are  described  and  classified,  and  their  special 
adaptations  indicated.  A  chapter  is  devoted  to  the  study  of 
the  characteristics  of  the  materials  used  by  the  engineer  in  the 
construction  of  steam-generators,  and  another  to  the  strength 
of  these  metals  in  their  several  forms  and  compositions,  the 
methods  of  adaptation  to  the  purposes  of  construction,  and  to 


869480 


IV  PREFACE. 

the  statement  of  the  precautions  to  be  observed  in  their  intro- 
duction into  so  important  a  structure.  Another  chapter  is 
appropriated  to  the  examination  of  the  composition  and  rela- 
tive values  of  the  various  available  fuels,  and  their  economical 
use  in  the  production  of  steam.  These  chapters  on  the  mate- 
rials and  their  characteristics  are  adapted  mainly  from  the 
notes  of  lectures  from  which  the  larger  work  of  the  Author — 
u  Materials  of  Engineering" — was  compiled.  It  has  been  the 
endeavor  of  the  Author  to  make  this  introductory  portion  of 
the  book  exceptionally  complete,  as  it  is  the  foundation  of  all 
that  follows,  and  is  a  branch  of  the  subject  to  which  much  at- 
tention is  rarely  given  in  treatises  of  this  character.  Follow- 
ing this  part  of  the  work  are  chapters  upon  the  laws  of  ther- 
modynamics, so  far  as  they  find  application  in  the  subsequent 
portion  of  the  work,  as,  for  example,  in  the  determination  of 
the  magnitude  of  the  stock  of  heat-energy  stored  in  steam, 
and  in  the  calculation  of  the  constants  required  in  tabulation 
of  its  properties;  and  this  part  of  the  scheme  is  introductory 
to  a  study  of  the  properties  of  water  in  its  several  character- 
istic forms, — solid,  liquid,  gaseous, — and  especially  of  the  essen- 
tial attributes  of  steam  at  the  pressures  and  temperatures 
which  are  customarily  met  with  in  every-day  practice.  The 
tables,  however,  which  are  here  given  are  carried  up  to  a  range 
of  pressure  and  of  temperature  far  exceeding  those  in  common 
use,  and  it  is  thought  are  sufficiently  complete  to  serve  their 
purpose  for  many  years,  notwithstanding  the  unintermitted 
progress  in  the  direction  of  higher  pressures  which  is  now  ob- 
served, and  which  is  not  likely  soon  to  completely  cease.  In 
these  tables  the  constants  of  Rankine  are  adopted,  not  so 
much  because  it  is  considered  by  the  Author,  if  we  may  judge 
from  what  is  to-day  known  on  this  subject,  that  they  are  quite 
as  likely  to  be  correct  as  any  others ;  but  for  the  reason  that 
they  have  become  so  generally  accepted  among  engineers,  and 
differ  so  little  from  the  best  values  taken  by  earlier  authorities, 
that  it  is  probably  wisest  and  safest  to  retain  them — at  least 
until  the  exact  quantities  are  better  settled  than  to-day.  It  is 
certain  that  the  differences  in  the  magnitudes  now  taken  for 
the  heat-equivalent,  for  example,  and  between  those  values 


PREFACE.  V 

and  the  exact  figures,  are  too  small  to  be  of  moment  to  the  en- 
gineer in  the  daily  operations  of  professional  work.  Rankine's 
reconstruction  of  Regnault's  results  are  here  accepted,  also  ; 
and  Buel's  tables,  the  only  tables  known  to  the  Author  in 
which  this  correction  has  been  applied,  are,  with  the  consent 
of  their  author  and  his  publishers,  here  given.  The  tables  of 
Porter,  published  in  his  treatise  on  the  Richards  Steam-en- 
gine Indicator,  may  be  used  where  separate  tables  in  con- 
venient and  compact  form  are  desired.  The  differences  to  be 
noted  between  the  latter,  which  are  compiled,  with  careful  re- 
vision, directly  from  Regnault,  and  those  of  Rankine  are  not 
great;  but  the  engineer  should  use  either  the  one  or  the  other 
exclusively  in  any  one  piece  of  work. 

In  the  study  of  the  methods  and  principles  of  designing 
steam-boilers,  an  attempt  is  made  to  collate  the  most  essential, 
and  to  apply  them  to  the  proportioning  of  the  best  forms  of 
boilers  now  familiar  to  the  engineer.  This  part  of  the  work 
is  of  great  importance  to  the  designing  engineer,  and  it  has 
been  the  endeavor  to  give  this  treatment  of  it  a  shape  that 
will  prove  at  once  sufficient  for  its  purpose,  and  yet  fairly  con- 
cise and  very  definite.  It  includes  chapters  on  the  design  of 
the  chimney  and  other  accessories,  and  on  specifications  and 
contracts — subjects  rarely  touched  upon  in  earlier  manuals. 
The  chapters  on  the  operation  and  care  of  boilers,  and  their 
management  generally,  is  largely  based  upon  a  somewhat  ex- 
tensive personal  experience  during  earlier  life,  on  the  part  of 
the  Author,  when  he  was  engaged,  first  in  the  business  of  con- 
stuction,  and  later  in  actual  practice,  during  the  civil  war,  as  a 
member  of  the  corps  of  U.  S.  Naval  Engineers,  as  well  as 
during  two  decades  of  desultory  practice  as  a  consulting  en- 
gineer since  that  time.  It  is  hoped  that  it  may  prove  well 
suited  to  meet  the  needs  of  the  class  of  young  men  to  whom  it 
is  addressed. 

In  the  chapter  on  trials  of  steam-boilers,  the  methods  re- 
ported favorably  to  the  American  Society  of  Mechanical  En- 
gineers are  adopted  as  standard,  and  the  report  of  the  com- 
mittee is  taken  almost  bodily  into  the  text.  As  this  report, 
in  part,  was  prepared  by  the  Author  from  his  lecture-notes 


VI  PREFACE. 

largely,  and  in  consultation  with  the  several  distinguished  en- 
gineers associated  with  him  on  that  committee,  it  may,  very 
probably,  be  admitted  that  this  wholesale  quotation  is  fully 
justified.  The  report  will  be  found  published  in  full  in  the 
Transactions  of  that  Society,  together  with  the  discussion 
brought  out  by  its  presentation. 

The  chapter  on  explosions  is  already  in  print,  with  a  few 
additions,  as  a  treatise  on  the  subject,  published  by  Messrs.  J. 
Wiley  &  Son.  It  was  considered  that  such  publication  would 
very  possibly  prove  of  some  service  in  preventing  this  proba- 
bly absolutely  preventable  class  of  disasters,  and  that  it  would 
secure  a  wider  circulation,  and  do  so  much  the  more  good,  if 
printed  as  a  separate  monograph. 

The  work,  as  a  whole,  is  a  larger  treatise  than  could  be  used 
profitably  in  the  average  technical  school ;  but  it  is  thought 
that  it  may  find  its  place  in  the  special  schools  of  mechanical 
engineering,  in  those  which  are  properly  entitled  to  be  called 
professional  schools,  giving  a  training  which  really  fits  the 
student  who  may  succeed  in  passing  through  them  for  en- 
trance into  the  ranks  of  a  profession  which  demands  of  its 
cadets  a  more  complete  preparation  and  a  higher  standing 
than  any  other,  even  among  the  distinctively  so-called  learned 
professions.  The  Author  is  fully  conscious  of  the  vast  discrep- 
ancy between  his  aim  and  his  accomplishment  ;  but  he  hopes 
that  the  book  may  be  of  some  service,  nevertheless,  to  many 
engineers,  old  and  young. 

SIBLEY  COLLEGE,  CORNELL  UNIVERSITY, 
January,  1888. 


CONTENTS. 


CHAPTER  I. 
HISTORY   OF  THE  STEAM-BOILER;  STRUCTURE;   DESIGN. 

SEC.  PAGE 

1.  Office  of  the  Steam  Boiler, r 

2.  Development  of  Standard  Forms,          .......  2 

3.  The  older  Types  of  Boiler 4 

4.  Special  purposes  and  modern  Types,     .         ...         .         .         .         .  7 

5.  Method  and  Limit  of  Improvement,      .                  10 

6.  Principles  involved  in  designing, n 

7.  Production,  transfer,  and  storage  of  Heat,    ......  12 

8.  Utilization  of  Heat, 15 

9.  Safety  in  operation, 18 

10.  Appurtenances  of  Steam  Boilers, 18 

11.  Classification  of  Boilers,        ........'.  19 

12.  Modern  Standard  Forms,      .........  20 

13.  Mixed  Types 20 

14.  Mixed  Application 20 

15.  Common  "  Shell  "  Stationary  Boilers,           ......  21 

16.  The  Locomotive  Boiler.         .........  26 

17.  Marine  Boilers;  older  Forms,         ........  29 

18.  Marine  Water-tube  Boilers,            .                  30 

19.  The  Scotch  Boiler,         ..........  32 

20.  Sectional  Boilers, 35 

21.  Marine  sectional  Boilers,       .........  38- 

22.  Periods  of  Introduction,         .........  39 

23.  Special  Forms  of  Boiler.        .........  42 

24.  Problems  in  Design  and  Construction, 43 

25.  Problems  in  the  Use  of  Boilers,     ........  43 

26.  General  Methods  of  Solution 43 

CHAPTER  II. 

MATERIALS    OF    STEAM-BOILERS;     STRENGTH    AND    OTHER 
CHARACTERISTICS. 

27.  Quality  of  Materials  required, 45 

28.  Principles  relating  to  Strength, 45 

29.  Tenacity,  Elasticity.  Ductility,  Resilience,    ......  56 


Vlll  CONTENTS. 


30.  Characteristics  of  Iron,  physical  and  chemical, 57 

31.  "         "          "  Steel,          .                  63 

32.  Effect  of  Variation  of  Form,           ........  64 

33.  "       "   Method  of  Treatment,    .         ......         .70 

34.  "       "  Time  and  Margin  of  Stress,    .......  74 

35.  Method  of  detecting- Overstrain,    ........  81 

36.  Effect  of  Temperature, 83 

37.  Crystallization  and  Granulation,   ........  go 

38.  Iron  and  Steel  compared, 92 

39.  Grades  and  Qualities  of  Iron  Boiler-plate,    ......  94 

40.  Manufacture  of  Iron  and  Steel  plate,  .          ......  96 

41.  Methods  of  Test  of  Iron  and  Steel,        .......  98 

42.  Results  of  Tests,    ...........  104 

43.  Specifications  of  Quality, 108 

44.  Choice  for  Various  Parts,      .........  112 

45.  Methods  of  Working,    ......          ....  113 

46.  Special  Precautions  in  using  Steel,         .......  113 

47.  Rivets  and  Rivet  Iron  and  Steel,  .         .         .         .         .         .         .114 

48.  Sizes,  Forms,  and  Strength  of  Rivets,            ......  115 

49.  Strength  of  riveted  Seams;  Helical  Seams,  .         .         .         .         .         .117 

50.  Punched  and  Drilled  Plates,          .         ...         .         .         .         .         .  123 

51.  Steam-riveting  and  Hand-riveting,        .......  125 

52.  Welded  Seams,       ...........  127 

53.  "  Struck-up"  or  Pressed  Shapes,   ........  127 

54.  Cast  and  Malleableized  Iron,  Brass,  and  Copper,         .         .         .         .127 

55.  Shells  of  Boilers, 129 

56.  Flues,  Flanged  and  Corrugated,   ........  140 

57.  Stayed  Surfaces,  Stays  and  Braces,       .......  144 

58.  Relative  Strength  of  Shell  and  Sectional  Boilers,          ,         .         .         .148 

59.  Loss  of  Strength  and  Ductility  of  Metal,       ......  149 

60.  Deterioration  of  Boilers,        .         .         .         .         .         .         .         .         .150 

61.  Inspection  and  Test  of  Boilers,     ........  151 

CHAPTER  III. 
THE   FUELS   AND   THEIR   COMBUSTION. 

62.  Combustion  defined  ;   Perfect  Combustion,           .....  152 

63.  Fuels;  Coal  defined,     ..........  153 

64.  Anthracite  Coals, 155 

65.  Bituminous  Coals,        ..........  156 

66.  Lignites, 158 

67.  Peat  or  Turf, 159 

68.  Wood, 159 

69.  Coke,            ............  160 

70.  Charcoal,      ............  162 

71.  Pulverized  Fuel, 164 


CONTENTS.  ix 

SEC.  PAGE 

72.  Liquid  Fuels, .165 

73.  Gaseous  Fuels,     .                  •         •        •  167 

74.  Artificial  Fuels,    .         . 168 

75.  Heating  Power  of  Fuels, 169 

76.  Temperature  of  the  Fire,      . 172 

77.  Minimum  Air  required,        .         .         .         .         .     -    .         .         .         .  178 

78.  Temperature  of  Products  of  Combustion,   .         .         .         .         .         .179 

79.  Rate  of  Combustion, 184 

80.  Efficiency  of  Furnace,           .........  185 

81.  Economy  of  Fuel,         ..........  187 

82.  Weather  Wastes,           ..........  191 

83.  Composition  of  Fuels, 192 

84.  Heating  Effects  of  Fuels, 194 

85.  Composition  of  Ash, 200 

86.  Commercial  Value  of  Fuels,          ........  201 

87.  Furnace  Management,          .........  204 

88.  Adaptation  of  Boiler,  Furnace,  and  Fuel,    ......  206 

CHAPTER   IV. 

HEAT;     ITS     NATURE,    PRODUCTION,     MEASUREMENT     AND     TRANSFER; 
EFFICIENCY   OF  HEATING  SURFACE. 

89.  Nature  of  Heat,  ...........  207 

90.  Methods  of  Production  ;  Combustion,          ......  208 

91.  Temperatures  ;  Quantities  of  Heat  ;  Specific  Heat,     .         .        .         .210 

92.  Thermometry  ;  Calorimetry, 214 

93.  Transfer  of  Heat 215 

94.  Radiation  of  Heat,       ..........  216 

95.  Conduction,          ...........  217 

96.  Convection,           ...........  219 

97.  Transfer  of  Heat  in  the  Steam  Boiler, 220 

98.  Formulas  for  Efficiency  of  Heating  Surfaces,  and  Area  of  Cooling 

Surfaces,       ...........  221 

99.  Effect  of  Incrustation  and  Deposits, 228 

CHAPTER   V. 
HEAT  AS  ENERGY;  THERMODYNAMICS. 

ico.  Heat  as  a  form  of  Energy, 229 

101.  Energetics  ;  Heat-energy  and  Molecular  Velocity,      ....  233 

102.  Heat-energy  as  related  to  Temperature,      ......  235 

103.  Quantitative  measure  of  Heat-energy,          ......  236 

104.  Heat  transformations,           .........  237 

105.  Heat  and  Mechanical  Energy, 237 

106.  Thermodynamics  defined, 238 


X  CONTENTS. 

SEC.  PAGE 

107.  First  Law  of  Thermodynamics, 239 

108.  Second  Law  of  Thermodynamics,        .......  240 

109.  Molecular  Constitution  of  Bodies,       .......  241 

no.  Solids,  Liquids  and  Gases  defined  ;  the  perfect  gas,   ....  241 

in.   Heat  and  Matter;  Specific  Heats,        .......  242 

112.  Sensible  and  Latent  Heats,          ........  243 

113.  Latent  Heat  of  Expansion,           ........  243 

114.  Latent  Heats  of  Fusion  and  Vaporization,  ......  244 

115.  Distribution  of  Heat-energy,         ........  244 

116.  Application  of  First  Law  ;  Equations,          ......  245 

117.  Application  of  Second  Law, 247 

118.  Computation  of  Internal  and  External  Forces  and  Work,  .         .        .  248 


CHAPTER   VI. 

STEAM  ;    VAPORIZATION  ;     SUPERHEATING ;    CONDENSATION  ;    PRESSURE 
AND    TEMPERATURE. 

119.  Steam  Generation  and  Application,     .......  252 

120.  Properties  of  Water;  Water  as  a  Solvent, 253. 

121.  Composition  and  Chemistry  of  Water,         ......  254 

122.  Sources  and  Purity  of  "  fresh"  Water,          ......  255 

123.  Sea  WTater  ;  Deposits  and  Remedies, 256 

124.  Technical  Uses  of  Water;  Filtration,           ......  260 

125.  Water-analysis,              .....                   ....  261 

126.  Purification  of  Water,           .........  262 

127.  Physical  Characteristics  of  Water, 263 

128.  Changes  of  Physical  State,           .         .         .         .                  .         .         .  265 

129.  The  "  Critical  Point," 265 

130.  The  "Spheroidal  State;"  Superheated  Water 268 

131.  Vaporization;  Superheating  Steam,              .         .                   .         .         .  269 

132.  Thermal  and  Thermodynamic  Relations,    ......  270 

133.  Internal  Pressures  and  Work;  Total  and  Latent  Heats,      .         .         .  271 

134.  Computation  of  Internal  Work  and  Pressure,            ».         .         .         ,  271 

135.  Specific  Volumes  of  Steam  and  Water, 272 

136.  Relations  of  Temperatures,  Pressures  and  Volumes,  ....  273 

137.  Specific  Heats  of  Water  and  Steam,     .......  275 

138.  Computation  of  Latent  and  Total  Heats,    ......  276 

139.  Factors  of  Evaporation,        .........  278 

140.  Regnault's  Researches  and  Methods,            ......  280 

141.  Regnault's  Tables,        ..........  281 

142.  Stored  Energy  in  Steam;  Tables, 285 

143.  Curves  of  Energy, 289 

144.  Power  of  Steam ;  of  Boilers,         .         .         .         .         .         .         .         .  291 

145.  Horse-power  of  Boilers,        .........  292. 


CONTENTS.  XI 


CHAPTER  VII. 
CONDITIONS  CONTROLLING   BOILER  DESIGN. 

SEC.  PAGE 

146.  The  Problem  stated,             3°° 

147.  Selection  of  Type  and  Location, 300 

148.  Choice  of  Fuel;  Method  of  Combustion, 302 

149.  Conditions  of  Efficiency ;  Pressure  chosen, 303 

150.  Principles  of  Design,    ..........  304 

151.  Controlling  Ideas  in  Construction,       .......  307 

152.  Factors  of  Safety ;  Efficiency  and  Cost,        ......  311 

153.  Water-tubes  and  Fire-tubes,         ........  312 

154.  Shell  and  Sectional  Boilers,          .         .         .         .         .         .         .         .  314 

155.  Natural  and  Forced  Draught,       ........  314 

156.  Special  conditions  affecting  Design, 317 

157.  Chimney  Draught 31? 

158.  Size  and  Form  of  Chimney,         ........  322 

159.  Furnace  and  Grate,      .         .         .         .         .         ....         .         .  329 

160.  Relative  areas  of  Chimney,  Flues  and  Grate,      .....  334 

161.  Common  Proportions  and  Work  of  Boiler,          .....  335 

162.  Usual  rates  of  Evaporation,         ........  338 

163.  Quality  of  Steam  and  Efficiency, 338 

164.  Boiler  Power;  Number  and  Size, 340 

165.  Standard  Sizes  of  Tubes;  Spacing, 341 

166.  Details  of  the  Problem, 345 

CHAPTER   VIII. 
DESIGNING   STEAM   BOILERS. 

167.  General  Considerations 34° 

168.  Parts  defined  ;  Common  Matters  of  Detail, 346 

169.  Designing  the  Plain  Cylinder  Boiler, 350 

170.  Stationary  Flue  Boilers,       . 354 

171.  Cylinder  Tubular  Boilers,    .         .         .         .         .         .         .         .         .  358 

172.  Marine  Flue  Boilers,    ..........  301 

173.  Marine  Tubular  Boilers, 362 

174.  Sectional  and  Water-tube  Boilers, 364 

175.  Upright  and  Portable  Boilers, 369 

176.  Locomotive  Boilers,    ........*•  371 

CHAPTER   IX. 
ACCESSORIES  ;   SETTING ;   DESIGN  OF  CHIMNEYS. 

177.  Setting  Steam  Boilers;  Suspension, 3?6 

178.  Covering 380 

179.  Form  and  Location  of  Bridge- wall, .381 


Xll  CONTENTS. 

SEC.  PAOH 

180.  Disposition  of  Flues,  .         .         .         .         .         .         .         .         .381 

181.  Location  and  Form  of  Dampers,          .......  381 

182.  Steam  and  Water  pipes, 383 

183.  Safety  Valves 385 

184.  Feed  Apparatus  ;  Heaters,           ........  392 

185.  Steam  Gauges,  Fusible  Plugs,  and  minor  accessories,         .         .         .  393 

CHAPTER   X. 
CONSTRUCTION   OF   BOILERS. 

186.  Methods  and  Processes;  Drawings 400 

187.  Apparatus  and  Machinery,  .         .         .         .         .         .         .         .         .  401 

188.  Shearing;  Planing;  Fitting,          ........  402 

189.  Flanging  and  Pressing;  Drilling  and  Punching,           ....  402 

190.  Forming  bent  parts,     ..........  403 

191.  Riveting  and  Riveting  Machines;  Welding,         .....  404 

192.  Setting  Tubes  and  Flues;  Staying 413 

193.  Chipping  and  Calking,          .........  417 

194.  Assembling 420 

195.  Inspection,   ............  420 

196.  Testing  Steam  Boilers,         .........  422 

197.  Sectional  Boilers,         ..........  423 

198.  Transportation  and  Delivery 424 

CHAPTER   XI. 
SPECIFICATION  ;   CONTRACTS  ;   INSPECTION. 

199.  Purpose  of  Specification  and  Contract, 425 

200.  The  Contract, .  426 

201.  Form  of  Specifications,  generally,        .         .         .         .         .         .         .  427 

202.  Specification  for  Steam  Boilers,   ........  427 

203.  Sample  Specifications,  ..........  427 

204.  Specification  of  Quality  and  Tests  of  Metal,         .....  436 

205.  Duties  of  the  Inspector, 43§ 

CHAPTER  XII. 
OPERATION   AND   CARE   OF   BOILERS. 

206.  General  Management, 44° 

207.  Starting  Fires  and  getting  up  Steam,  .         .         .         .         .        .         .  441 

208.  Managing  Fires,  ...........  442 

209.  Use  of  various  kinds  of  Fuel,       .         ,         .         .         .         .         .         »  444 

210.  Liquid  and  Gaseous  Fuels,  .                   .......  444 

211.  Solid  Fuels. 44^ 


CONTENTS.  Xlll 

SEC.  PAGE 

212.  Operation  of  the  Boiler, 445 

213.  Forced  Draught 44$ 

214.  Closed  and  Open  Fire-rooms,       ........  44$ 

215.  Control  of  Steam  Pressures, 449 

216.  Regulation  of  Water-supply, 449 

217.  Emergencies,        ...........  45° 

218.  Low  Water, 45<> 

219.  Priming;  Sudden  Stopping,          ........  451 

220.  Fractured  Seams;  Leaky  tubes,  ........  453 

221.  Deranged  Safety  Valves;  Excessive  Pressure, 454 

222.  General  Care  of  Boilers,      .........  454 

223.  Chemistry  of  Corrosion,       .........  454 

224.  Method  of  Corrosion,  .         .         .         .         .         .         .         .         .         .  455 

225.  Durability  of  Iron  and  Steel,        ........  457 

226.  Preservation  of  Iron,  ..........  45§ 

227.  Paints  and  Preservatives;  Coverings 458 

228.  Leakage;  Contact  with  Setting,  .         . 461 

229.  Galvanic  Action,           ..........  462 

230.  Incrustation;  Sediment,       .........  462 

231.  Repairs, 465 

232.  Inspection  and  Test,    ..........  466 

233.  General  Instructions, 469 

CHAPTER   XIII. 
EFFICIENCIES   OF  STEAM   BOILERS. 

234.  Efficiencies  of  the  Steam  Boiler, 472 

235.  Measures  of  Efficiency,         .........  473 

236.  Efficiency  of  Combustion,    .          .         . 473 

237.  Efficiency  of  Transfer  of  Heat,    ........  473 

238.  Net  Efficiency,     ...........  473 

239.  Finance  of  Efficiency, 474 

240.  Commercial  Efficiency, 474 

241.  Algebraic  Theory  of  Efficiencies, 476 

242.  Theory  of  Commercial  Efficiency,        .         .         .         .         .         .         .  477 

243.  Efficiency  of  a  Given  Plant,         . 481 

CHAPTER  XIV. 
STEAM-BOILER   TRIALS. 

244.  Purposes  of  Boiler  Trials,             ........  484 

245.  Test  of  Value  of  Fuel, 485 

246.  Determination  of  Value  of  Boiler,        .......  485 

247.  Evaporative  Power  of  Fuels,         ........  485 

248.  Analysis  of  Fuels,         ..........  486 


XIV  CONTENTS. 

SEC.  PAGE 

249.  Efficiency  and  Economy  of  Fuel, •   .         .  487 

250.  Relative  Values  of  Boilers,           . 489 

251.  Variation  of  Efficiency  with  Consumption  of  Fuel  and  Size  of  Grate,  489 

252.  Relation  of  Area  of  Heating  Surface  to  Economy,      ....  490 

253.  Combined  Power  and  Efficiency,         .......  490 

254.  Apparatus  and  Methods  of  Test,          .......  490 

255.  Standard  Test  trials,             .........  492 

256.  Instructions  and  Rules  for  Standard  Method,      .....  493 

257.  Precautions;  Blanks  and  Record,        .......  502 

258.  Results  of  Test-trials, 504 

259.  Quality  of  Steam,         .         .         ...         .         .         .         .         .         .517 

260.  Form  of  Barrel  Calorimeter  and  use,           ......  519 

261.  Theory  of  Calorimeters,       .         .         .         .         .         .         .         .         .521 

262.  Records  ;    Errors,         ..........  523 

263.  The  Coil  Calorimeter,          .........  524 

264.  The  Continuous  Calorimeter,      ........  527 

265.  Analysis  of  Gases  ;  Form  of  Apparatus,      ......  531 

266.  Efficiency  as  indicated  by  Gas-analysis,       .                  .         .         .         .  535 

267.  Draught  Gauges,          ..........  535 

CHAPTER   XV. 
STEAM-BOILER  EXPLOSIONS. 

268.  Steam-boiler  Explosions,     .........  538 

269.  Energy  stored  in  Boilers,    .         .         .         .         .         .         .         .         .  541 

270.  Energy  of  Steam  alone,        .........  548 

271.  Explosions   denned  and  described ;    Fulminating    Explosions  ;    Col- 

lapsed Flues  ;  Bursting,            . 549 

272.  Causes  of  Explosion  :    Probable  ;  Possible,  and  unusual  ;  improba- 

ble and  absurd,        ..........  550 

273.  Statistics  of  Explosions  and  Causes, 553 

274.  Theories  and  Methods  of  Explosion,            ......  558 

275.  Colburn's  Theory  of  Explosions,          .......  559 

276.  Lawson's  and  other  Experiments         .......  561 

277.  Energy  stored  in  heated  metal,             .......  567 

278.  Strength  of  heated  metal,              ........  568 

279.  Low-water  ;  Causes  and  Consequences, 568 

280.  Sediment  and  Incrustation,           ........  574 

281.  Energy  stored  in   superheated  water;    Experiments  of  Donny  and 

Dufour  ;  De-aeration  of  water,         .......  578 

282.  The  Spheroidal  State;  Leidenfrost's  and  Boutigny's  Experiments,     .  583 

283.  Steady  rise  of  Pressure,        .........  589 

284.  Relative  Security  of  Boilers,         .         .         .         .         .         .         .         .  502 

285.  Defects  of  Design,        ..........  593 

286.  Defective  Construction,                  596 

287.  Developed  Weakness  ;  Corrosion,       .         .         .  601 


CONTENTS.  XV 

SEC.  PAGE 

288.  General  and  Local  Decay, 604 

289.  Methods  of  Corrosion  and  Decay  ;  Grooving  or  Furrowing,       ,        .  606 

290.  Differences  of  Temperatures, 609 

291.  Management  of  Boilers,      .........  612 

292.  Emergencies  ;  Precautions,          . .614 

293.  Results  of  Explosions  ;  Causes;  Examples,                  .         .  616 

294.  Experimental  Explosions  and  Investigations,     .....  633 

295.  Conclusions, 642 


APPENDIX. 

TABLE    I. — Properties  of  Steam,        ....  ...    646 

"       la. — Regnault's  Table,     .        -        ,        .        .        .        .        .        .653 

"      II. — Energy  in  Water  and  Steam,  .......     656 

INDEX,        ...,.,.,....  659 


THE    STEAM-BOILER. 


CHAPTER   I. 

HISTORY   OF  THE   STEAM-BOILER — ITS   STRUCTURE. 

I.  The  Office  of  a  Steam-boiler  is  to  transfer  the  heat- 
energy  produced  by  the  combustion  of  fuel  to  the  mass  of  en- 
closed water,  and,  by  the  conversion  of  the  latter  into  steam, 
to  store  that  energy  in  available  form  for  use,  as  in  the  steairu 
engine. 

The  source  of  this  energy  was,  originally,  that  existing  in 
the  rays  of  the  sun,  and,  by  the  action  of  chemical  affinity  as 
exhibited  in  the  growth  of  vegetation,  it  has  been  transformed 
from  its  kinetic  form,  in  heat  and  light  rays,  to  the  potential 
form,  as  now  found  in  the  recent  or  fossil  fuels  of  forest  and 
coal-bed. 

The  process  of  absorption  and  storage  of  heat-energy  in 
vegetable  matter  is  reversed,  in  the  furnace,  in  the  combustion 
of  the  fuel ;  and  the  combination  of  the  carbon  and  hydrogen, 
constituting  the  familiar  hydrocarbons,  with  the  oxygen  of  the 
air  entering  the  "  firebox,"  retransforms  their  stored,  poten- 
tial, energy  into  the  available,  kinetic,  form  of  heat-motion,  and 
it  is  then  applied  to  the  elevation  of  the  temperature  of  the 
gaseous  products  of  combustion  and  of  the  nitrogen  passing 
through  the  boiler.  By  conduction  and  convection,  and  by 
radiation,  in  part,  this  heat  is  next  transferred  to  the  water  in 
the  boiler,  raising  its  temperature,  evaporating  it,  and  "  making- 
steam"  at  a  temperature  fixed  by  the  pressure  under  which  the 
operation  is  carried  on.  By  the  formation  of  steam,  a  part  of 
the  heat  is  converted  once  more  into  the  potential  form  by  that 
method  of  performance  of  "  internal  work"  in  the  separation  of 
molecule  from  molecule,  against  the  resistances  due  to  cohesive 
forces,  which  measures  the  "latent  heats"  of  evaporation  and  of 


2  THE   STEAM-BOILER. 

expansion;  while  ^th&  rera^ink%rj  ts  fthe  sensible  heat  of  the 
steam.  Thus  tlie^fluid  sit  or  ed  in  the^steam-boiler  is  a  reservoir 
of  energy  which \i«»  *itJa,vv£T^iipGFi  by^the^  ^team-engine  when  the 
latter  is  set  in  operation  to  transform  that  heat-energy  into  me- 
chanical energy ;  and  the  steam  sent  from  the  boiler  to  the  en- 
gine conveys  to  the  latter  this  energy  in  the  two  forms  of 
sensible  and  of  latent  heat,  or  of  actual  and  potential  energy. 

The  steam-boiler  should  be  capable  of  thus  producing,  stor- 
ing, and  delivering  heat-energy,  in  maximum  quantity,  and 
with  maximum  economy  and  safety.  In  other  words,  the 
steam-boiler  should  produce  steam  in  the  largest  practicable 
quantity,  with  the  least  possible  expenditure  of  fuel  and  of 
money,  and  with  perfect  safety. 

2.  The  Development  of  the  Standard  Forms  of  Steam- 
boiler  has  been  a  process  of  trial  and  error,  in  some  sense  one 
of  evolution  of  numerous  types,  and  of  the  survival  of  the  fit- 
test, extending  over  many  years.  In  the  earlier  days  of  the 

steam-engine  the  shapes  assum- 
ed were  invariably  simple,  and 
comparatively  easy  of  construc- 
tion. Thus  the  boiler  shown 
by  Hero  (Fig.  i),  in  his  "  Pneu- 
matica,"  two  thousand  years  ago, 
was  spherical ;  as  were  those  of 
many  later  engines,  all  being  evi- 
dently expected  to  be  capable 
of  sustaining  considerable  pres- 
sures.* 

Thus,  in  1601,  Giovanni  Bat- 
tista  della  Porta,  in  his  work 
"  Spiritali,"  described  an  appara- 
tus by  which  the  pressure  of 
steam  might  be  made  to  raise  a 
column  of  water,  and  the  method 

FIG.  i.— THE  GRECIA.N  IDEA  OF  THE 

STEAM-ENGINE.  of  operation  included  the  appli- 

cation of   the    condensation  of  steam    to  the   production  of  a 


History  of  the  Steam-engine.     R.  H.  Thurston. 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.        3 

vacuum  into  which  the  water  would  flow.  He  used  a  separate 
boiler.  Fig.  2  is  copied  from  an  illustration  in  a  later  edition 
of  his  work.* 


FIG.  2.— PORTA'S  APPARATUS,  A.D.  1601.  FIG.  3.— DE  CAUS'S  APPARATUS,  A.D.  1615. 

Again,  in  1615,  Salmon  de  Caus,  who  had  been  an  engineer 
and  architect  under  Louis  XIII.  of  France,  and  later  in  the 
employ  of  the  British  Prince  of  Wales,  published  a  work  at 
Frankfort,  entitled  "  Les  Raisons  des  Forces  Mouvantes  avec 
diverses  machines  tant  utile  que  plaisantes,"  in  which  he  illus- 
trated his  proposition,  "  Water  will,  by  the  aid  of  fire,  mount 
higher  than  its  level,"  by  describing  a  machine  designed  to 
raise  water  by  the  expanding  power  of  steam.  (See  Fig.  3.) 
This  consisted  of  a  metal  vessel  partly  filled  with  water,  and 
in  which  a  pipe  was  fitted  leading  nearly  to  the  bottom  and 
open  at  the  top.  Fire  being  applied,  the  steam,  formed  by  its 


I  Tre  Libri  Spiritali.     Napoli,  1606. 


THE   STEAM-BOILER. 


FIG.  4. — WORCES- 
TER'S   ENGINE,    A.D. 
1650. 


elastic  force,  drove  the  water  out  through  the  vertical  pipe, 
raising  it  to  a  height  depending  upon  either  the  wish  of  the 
builder  or  the  strength  of  the  vessel. 

In  Worcester's  apparatus,  also  (Fig.  4),  we  have  a  hardly 
less  simple  form  of  boiler,  the  operation  of  which  is  such  as  to 
render  it  subject  to  high  pressure. 

Steam  is  generated  in  the  boiler  D,  and 
thence  is  led  into  the  vessel  A,  already  nearly 
filled  with  water.  It  drives  the  water  in  a  jet 
out  through  a  pipe,  F  or  F ' .  The  vessel  A  is 
then  shut  off  from  the  boiler  and  again  filled  "  by 
suction'l  after  the  steam  has  condenseol^through 
the  pipe  G,  and  the  operation  is  repeated,  the 
vessel  B  being  used  alternately  with  A. 

The  separate  boiler,  as  here  used,  constitutes 
,a  very  important  improvement  upon  the  pre- 
ceding forms  of  apparatus,  although  the  idea 
was  original  with  Porta. 
Denys  Papin,  contemporary  with  the  Marquis  of  Worcester, 
and  a  distinguished  man  of  science  of  that  time,  invented  the 
common  lever  safety-valve,  and  applied  it  to  his  "  digester,"  as 
his  closed  vessel  for  cooking  under  pressure  was  called ;  he 
used  it  later  (1690)  on  the  steam-boil- 
ers connected  with  his  own  steam- 
engine.  It  has  been  continuously  in 
use  ever  since. 

3.  Forms  familiar  in  the  Last 
Century  approximate  modern 
types.  Thomas  Savery,  A.D.  1699, 
used  ellipsoidal  forms  in  his  then 
"  newly  invented  fire-engine,"  of 
which  Fig.  5  is  a  good  representa- 
tion, as  first  given  by  the  inventor 
himself,  in  the  "  Miner's  Friend." 
L  L  is  the  boiler,  in  which  steam 

is  raised,   and  through    the  pipes  O  O    FlG-  5-— SAVERY'S  ENGINE,  A.D.  1699. 

it  is  alternately  let  into  the  vessels  P  P. 

Suppose   it   to   pass  into  the  left-hand    vessel   first.      The 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.        5 

valve  M  being  closed  and  r  being  opened,  the  water  contained 
in  P  is  driven  out  and  up  the  pipe  5  to  the  desired  height, 
where  it  is  discharged. 

The  valve  r  is  then  closed,  and  also  the  valve  in  the  pipe  O. 
The  valve  M  is  next  opened,  and  condensing  water  is  turned 
upon  the  exterior  of  P  by  the  cock  F,  leading  water  from  the 
cistern  X.  As  the  steam  contained  in  P  is  condensed,  forming 
a  vacuum,  a  fresh  charge  of  water  is  driven  by  atmospheric 
pressure  up  the  pipe  T. 

Meantime,  steam  from  the  boiler  has  been  let  into  the  right- 
hand  vessel  P,  the  cock  W  having  been  first  closed  and  R 
opened.  The  charge  of  water  is  driven  out  through  the  lower 
pipe  and  the  cock  R,  and  up  the  pipe  5  as  before,  while  the 
other  vessel  is  refilling  preparatory  to  acting  in  its  turn. 

The  two  vessels  thus  are  alternately  charged  and  discharged 
as  long  as  is  necessary.  Savery's  method  of  supplying  his 
boiler  with  water  was  at  once  simple  and  ingenious. 

The  small  boiler  D  is  filled  with  water  from  any  convenient 
source,  as  from  the  stand-pipe  5.  A  fire  is  then  built  under  it, 
and,  when  the  pressure  of  steam  in  D  becomes  greater  than  in 
the  main  boiler  Z,  a  communication  is  opened  between  their 
lower  ends  and  the  water  passes  under  pressure  from  the 
smaller  to  the  larger  boiler,  which  is  thus  "  fed  "  without  inter- 
rupting the  work.  G  and  N  are  gauge-cocks  by  which  the  height 
of  water  in  the  boilers  is  determined,  and  these  attachments 
were  first  adopted  by  Savery. 

It  will  be  noticed  that  Savery,  like  the  Marquis  of  Worces- 
ter, and  like  Porta,  used  a  boiler  separate  from  the  water-reser- 
voir. 

A  working  model  was  submitted  to  the  Royal  Society  of 
London  in  1699,*  and  successful  experiments  were  made 
with  it. 

Newcomen's  engine,  of  1705  and  later,  superseded  the 
Savery  apparatus  in  consequence  of  his  adaptation  of  his  ma- 
chine to  the  use  of  low  (atmospheric)  pressure  steam,  quite  as 
much  as  because  of  its,  greater  economy.  By  introducing  the 

*  Transactions  of  the  Royal  Society,  1699. 


THE    STEAM-BOILER. 


beam-engine,  and  pumps  separate  from  the  steam-vessel,  he 

was  able  to  avoid  all  danger  of  explo- 
sion, using  his  steam  at  a  pressure  but 
little  exceeding  that  of  the  atmos- 
phere, and  applying  it  simply  to  the 
displacement  of  the  air,  preliminary  to 
the  production  of  a  vacuum.  It  thus 
became  safe  to  use  any  convenient 
form  of  steam-vessel,  and  in  Fig.  6  it 
is  seen  that  he  at  once  departed  most 
signally  from  those  shapes  which  had 
necessarily  been  earlier  used,  and  took 

FIG.  6.— NEWCOMERS  ENGINE  AND  advantage  of  this  freedom  in  design  to 

BOILER,  A.D.  1705.  ' 

secure  a  type  of  boiler  of  greater  pro- 
portional area  of  heating-surface,  as  shown  at  d,  and  conse- 
quently of  greater  economy  in  use  of  fuel.  It  is  seen  that  he 
used  gauge-cocks,  c  c,  and  safety-valves,  N. 

James  Watt's  first  boiler  illustrates  another  step  in  this 
latter  direction. 

In  this,  A,  Fig.  7,  the  "wagon-boiler,"  as  he  called  it,  the 


FIG.   7.— WATT'S  FIRST 
MODEL,  1765. 


FIG.  8.— OLIVER  EVANS'S  ENGINE,  1800. 


vessel  is  so  shaped  as  to  permit  flues  to  be  formed  on  either 
side,  as  well  as  below,  for  the  circulation  of  the  products  of 
combustion  backward  and  forward  from  end  to  end  of  the 
boiler. 

A  still  further  advance  is  illustrated  in  the  now  well-known 
"  Cornish  Boiler,"  Fig.  8,  as  used  by  Oliver  Evans  in  the  United 
States,  and  by  British  engineers  of  his  time  (1800),  of  which 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE. 


the  "  shell "  is  cylindrical,  and  through  which  a  single  flue,  of 
about  one  half  the  diameter  of  the  boiler,  passes  from  one  end 
to  the  other.  The  gases  traverse  this  flue  and  also  partly  en- 
velop the  exterior  of  the  shell,  thus  coming  in  contact  with  a 
comparatively  large  extent  of  heating-surface.  This  form  was 
followed  by  the  "two-flued"  Evans  or  Lancashire  boiler,  which 
was  a  cylinder  containing  two  flues,  each  about  one  third  its 
diameter,  and  by  others  in  which  the  number  of  flues  was  in- 
creased with  continually  decreasing  diameter,  and  with  con- 
stant gain  in  total  heating-surface  until  the  modern  types  of 
tubular  boiler  were  developed. 

4.  Special  Purposes  produce  the  Modern  Types  of 
boilers.  Thus  a  desire  to  secure  maximum  efficiency  produced 
the  tubular  boilers,  and  the  desire  to  secure  safety  the  so-called 
"  sectional  boilers."  As  early  as  1/93,  Barlow  invented,  and 


FIG.  9.— WATER-TUBE  BOILER  OF  FULTON  AND 
BARLOW,  1793. 


FIG.  10. — STEVENS'S  "  SECTIONAL" 
BOILER,  1804. 


with  Fulton  used,  the  "  water-tube"  boiler  (Fig.  9),  in  which  the 
water  circulates  through  the  tubes,  instead  of  around  them, 
as  in  "  fire-tube"  boilers.  This  was  the  pioneer  of  a  great  variety 
of  boilers  of  this  class. 

John  Stevens,  a  distinguished  statesman  as  well  as  engineer, 
of  the  early  part  of  the  nineteenth  century,  devised  another  ex- 
ample of  this  class,  shown  in  Fig.  10,  as  early  as  the  year  1804. 

The  inventor  says  in  his  specifications :  "  The  principle  of 
this  invention  consists  of  forming  a  boiler  by  means  of  a  system 
or  combination  of  small  vessels,  instead  of  using,  as  is  the  com- 
mon mode,  one  large  one  ;  the  relative  strength  of  the  materials 
of  which  these  vessels  are  composed  increasing  in  proportion  to 
the  diminution  of  capacity."  The  steamboat  boiler  of  1804  was 


THE   STEAM-BOILER. 

built  to  bear  a  working  pressure  of  over  fifty  pounds  to  the 
square  inch,  at  a  time  when  the  usual  pressures  were  from  four 
to  seven  pounds.  It  consists  of  two  sets  of  tubes,  closed  at  one 
end  by  solid  plugs,  and  at  their  opposite  extremities  screwed 
into  a  stayed  water  and  steam  reservoir,  which  was  strengthened 
by  hoops.  The  whole  of  the  lower  portion  was  inclosed  in  a 
jacket  of  iron  lined  with  non-conducting  material.  The  fire 


FIG.  ii. — GURNEY'S  STEAM  CARRIAGE,  1833. 

was  built  at  one  end,  in  a  furnace  inclosed  in  this  jacket.  The 
furnace-gases  passed  among  the  tubes,  down  under  the  body  of 
the  boiler,  up  among  the  opposite  set  of  tubes,  and  thence  to 
the  smoke-pipe.  In  another  form,  as  applied  to  a  locomotive 
in  1825,  the  tubes  were  set  vertically  in  a  double  circle  sur- 


FIG.  12. — STEPHENSON'S  LOCOMOTIVE,  1815. 

rounding  the  fire.     These  boilers  are  carefully  preserved  among 
the  collections  of  the  Stevens  Institute  of  Technology. 

Still  another  modification  of  this  type  is  illustrated  in  the 
boiler  used  by  Gurney  in  steam-carriages  (Fig.  1 1)  built  about 
the  years  1830-5,  in  which  the  steam-generator  consisted  of  bent 
steam-pipe  of  small  diameter  so  connected  with  steam  and  mud 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE. 


drums  as  to  make  a  very  efficient  as  well  as  safe  and  powerful 
boiler  for  use  where  lightness,  .strength,  and  safety  were  essen- 
tial characteristics. 

Similarly,  the  special  demands  of  locomotive  construction 
were  not  fully  met  by  the  single-flue  boiler  first  used  by  George 
Stephenson  (Fig.  12)  and  by  his  colleagues  in  1815,  and  up  to 


FIG.  13. — STOCKTON  AND  DARLINGTON  ENGINE  No.  i,  1825. 

the  time  of  construction  of  the  Stockton  and  Darlington  Rail- 
way in  1825  (Fig.  13),  an  example  of  which  is  still  preserved  in 
the  first  engine  built  for  that  road.  At  the  opening  of  the  Liv- 
erpool and  Manchester  Railway  (1829),  Stephenson's  Rocket 
was  given  the  multitubular  boiler,  a  form  which  had  grown  into 
shape  in  the  hands  of  several  inven- 
tors.* This  boiler  was  three  feet  in 
diameter,  six  feet  long,  and  had 
twenty-five  three-inch  tubes,  extend- 
ing from  end  to  end  of  the  boiler. 
The  steam-blast  was  carefully  adjusted 
by  experiment,  to  give  the  best  effect. 
Steam-pressure  was  carried  at  fifty 
pounds  per  square  inch. 

The  average  speed  of  the  Rocket 
on  its  trial  was  fifteen  miles  per  hour,       FlG-  H--THE  ROCKET,  1829. 
and  its  maximum  was  nearly  double  that — twenty-nine  miles 
an  hour;  and   afterward,  running  alone,  it  reached  a  speed  of 
thirty-five  miles. 


*  Barlow  and  Fulton,    1795;    Nathan   Read,  Salem,    United  States,   1796; 
Booth  of  England,  and  Seguin  of  France,  about  1827  or  1828. 


10  THE   STEAM-BOILER. 

The  shares  of  the  company  immediately  rose  ten  per  cent 
in  value.  The  combination  of  the  non-condensing  engine  with 
a  steam-blast  and  the  multitubular  boiler,  designed  by  the  clear 
head  and  constructed  under  the  eye  of  an  accomplished  engi- 
neer and  mechanic,  made  steam  locomotion  so  evident  and 
decided  a  success,  that  thenceforward  its  progress  has  been  un- 
interrupted and  wonderfully  rapid.* 

The  special  requirements  of  stationary  steam-engine  con- 
struction and  operation,  and  of  steam  navigation,  have,  from 
these  primitive  types  and  forms,  developed  in  the  course  of 
years  the  several  now  common  and  standard  boilers  which  will 
be  later  described. 

5.  The  Method  and  Extent  of  Improvement  is  now  easily 
traced.  Looking  back  over  the  history  of  the  steam-engine,  we 
may  rapidly  note  the  prominent  points  of  improvement  and 
the  most  striking  changes  of  form  ;  and  we  may  thus  obtain 
some  idea  of  the  general  direction  in  which  we  are  to  look  for 
further  advance.f 

Beginning  with  the  machine  of  De  Caus,  at  which  point  we 
may  first  take  up  an  unbroken  thread,  it  will  be  remembered 
that  we  there  found  a  single  vessel  performing  the  functions  of 
all  the  parts  of  a  modern  pumping-engine  ;  it  was  at  once 
boiler,  steam-cylinder,  and  condenser,  as  well  as  both  a  lifting 
and  a  forcing  pump.  The  Marquis  of  Worcester,  and,  still 
earlier,  Da  Porta,  divided  the  engine  into  two  parts  ;  using  one 
part  as  a  steam-boiler,  and  the  other  as  a  separate  water-vessel. 
Savery  duplicated  those  parts  of  the  earlier  engine  which  acted 
the  several  parts  of  pump,  steam-cylinder,  and  condenser,  and 
added  the  use  of  the  jet  of  water  to  effect  rapid  condensation. 
Newcomen  and  Cawley  next  introduced  the  modern  type  of 
engine,  and  separated  the  pump  from  the  steam-engine  proper ; 
in  their  engine,  as  in  Savery's,  we  notice  the  use  of  surface- 
condensation  first,  and,  subsequently,  that  of  a  jet  of  water 
thrown  into  the  midst  of  the  steam  to  be  condensed.  Watt 
finally  effected  the  crowning  improvement  of  the  single-cylinder 

*  History  of  the  Steam-engine.     R.  H.  Thurston.     N.  Y.:  D.   Appleton  & 
Co. ,1878. 
f  Ibid. 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.      II 

engine,  and  completed  this  movement  of  differentiation  by 
separating  the  condenser  from  the  steam-cylinder,  thus  perfect- 
ing the  general  structure  of  the  engine. 

Here  this  movement  ceased,  the  several  important  processes 
of  the  steam-engine  now  being  conducted  each  in  a  separate 
vessel.  The  boiler  furnished  the  steam  ;  the  cylinder  derived 
from  it  mechanical  power ;  the  vapor  was  finally  condensed  in 
a  separate  vessel ;  while  the  power,  which  had  been  obtained 
from  it  in  the  steam-cylinder,  was  transmitted  through  still 
other  parts  to  the  pumps,  or  wherever  work  was  to  be  done. 

Watt  and  his  contemporaries  also  commenced  that  move- 
ment toward  higher  pressures  of  steam,  used  with  greater  ex- 
pansion, which  has  been  the  most  striking  feature  noticed  in 
the  progress  made  since  his  time.  Newcomen  used  steam 
of  barely  more  than  atmospheric  pressure,  and  raised  105,000 
pounds  of  water  one  foot  high,  with  a  pound  of  coal  consumed. 
Smeaton  raised  the  steam-pressure  to  eight  pounds,  and  in- 
creased the  duty  to  120,000.  Watt  started  with  a  duty  of 
double  that  of  Newcomen,  and  raised  it  320,000  foot-pounds 
per  pound  of  coal,  with  steam  at  ten  pounds.  To-day,  Cornish 
engines  of  the  same  general  plan  as  those  of  Watt,  but  worked 
with  forty  to  sixty  pounds  pressure,  expanding  three  to  six 
times,  bring  up  the  duty  to  600,000  foot-pounds ;  while  more 
modern  compound  engines  have  boilers  carrying  150  pounds 
(ten  atmospheres)  above  the  normal  air-pressure,  and  the  duty 
has  been  since  raised  to  above  1,200,000  foot-pounds  per  pound 
of  fuel  used. 

6.  The  Requisites  of  Good  Design  are  readily  prescribed 
and  defined  :  they  are  very  simple,  and  although  attempts  are 
almost  daily  made  to  obtain  improved  results  by  varying  the 
design  and  arrangement  of  heating-surface,  the  best  boilers  of 
nearly  all  makers  of  acknowledged  standing  are  practically 
equal  in  merit,  although  of  diverse  forms. 

In  making  boilers  the  effort  of  the  engineer  should  evidently 
be- 

ist.  To  secure  complete  combustion  of  the  fuel  without 
permitting  dilution  of  the  products  of  combustion  by  excess  of 
air. 


12  THE   STEAM-BOILER. 

2<d.  To  secure  as  high  temperature  of  furnace  as  possible. 

3d.  To  so  arrange  heating-surfaces  that,  without  checking 
draught,  the  available  heat  shall  be  most  completely  taken  up 
and  utilized. 

4th.  To  make  the  form  of  boiler  such  that  it  shall  be  con- 
structed without  mechanical  difficulty  or  excessive  expense. 

5th.  To  give  it  such  form  that  it  shall  be  durable,  under 
the  action  of  the  hot  gases  and  of  the  corroding  elements  of 
the  atmosphere. 

6th.  To  make  every  part  accessible  for  cleaning  and  repairs. 

7th.  To  make  every  part  as  nearly  as  possible  uniform1  in 
strength,  and  in  liability  to  loss  of  strength  by  wear  and  tear, 
so  that  the  boiler  when  old  shall  not  be  rendered  useless  by 
local  defects. 

8th.  To  adopt  a  reasonably  high  "  factor  of  safety"  in  pro- 
portioning. 

9th.  To  provide  efficient  safety-valves,  steam-gauges,  and 
other  appurtenances. 

loth.  To  secure  intelligent  and  very  careful  management. 

7.  Effective  Development,  Transfer,  and  Storage  of 
Heat,  in  the  best  possible  combination,  is  evidently  what  is 
demanded  in  the  operation  of  the  steam-boiler. 

In  securing  complete  combustion  an  ample  supply  of  air 
and  its  thorough  intermixture  with  the  combustible  elements 
of  the  fuel  are  essential  ;  for  the  second,  high  temperature  of 
furnace,  it  is  necessary  that  the  air-supply  shall  not  be  in  excess 
of  that  absolutely  needed  to  give  complete  combustion.  The 
efficiency  of  a  furnace  burning  fuel  completely  is  measured  by 


in  which  E  represents  the  ratio  of  heat  utilized  to  the  whole 
calorific  value  of  the  fuel  ;  T  is  the  furnace-temperature  ;  T 
the  temperature  of  the  chimney,  and  /  that  of  the  external  air. 
Hence  the  higher  the  furnace-temperature  and  the  lower  that 
of  the  chimney,  the  greater  the  proportion  of  available  heat. 
It  is  further  evident  that,  however  perfect  the  combustion, 


HISTO&*     OF   THE   STEAM-BOILER— ITS  STRUCTURE.      13 

no  heat  can  be  utilized  if  either  the  temperature  of  chimney  ap- 
proximates to  that  of  the  furnace,  or  if  the  temperature  of  the 
furnace  is  reduced  by  dilution  approximately  to  that  of  the 
chimney.  Concentration  of  heat  in  the  furnace  is  secured,  in 
some  cases,  by  special  expedients,  as  by  heating  the  entering 
air,  or,  as  in  the  Siemens  gas-furnace,  heating  both  the  combus- 
tible gases  and  the  supporter  of  combustion.  Detached  fire- 
brick furnaces  have  an  advantage  over  the  "fireboxes"  of 
steam-boilers  in  their  higher  temperature  ;  surrounding  the  fire 
with  non-conducting  and  highly  heated  surfaces  is  an  effective 
method  of  securing  more  perfect  combustion  and  high  furnace- 
temperature. 

In  arranging  heating-surface  the  effort  should  be  to  impede 
the  draught  as  little  as  possible,  and  so  to  place  them  that  the 
circulation  of  water  within  the  boiler  should  be  free  and  rapid 
at  every  part  reached  by  the  hot  gases. 

The  directions  of  circulation  of  water  on  the  one  side  and 
of  gas  on  the  other  side  the  sheet  should,  whenever  possible,  be 
opposite.  The  cold  water  should  enter  where  the  cooled  gases 
leave,  and  the  steam  should  be  taken  off  farthest  from  that 
point.  The  temperature  of  chimney-gases  has  thus  been  re- 
duced by  actual  experiment  to  less  than  300°  Fahr.,  and  an 
efficiency  equal  to  0.75  to  0.80  the  theoretical  is  attainable. 

The  extent  of  heating-surface  simply,  in  all  of  the  best 
forms  of  boiler,  determines  the  efficiency,  and  the  disposition 
of  that  surface  in  such  boilers  seldom  affects  it  to  any  great 
extent.  The  area  of  heating-surface  may  also  be  varied  within 
wide  limits  without  greatly  modifying  efficiency.  A  ratio  of 
25  to  I  in  flue  and  30  to  I  in  tubular  boilers  represents  the 
relative  area  of  heating  and  grate  surfaces  in  the  practice  of  the 
best-known  builders.  This  proportion  may  be  often  settled  by 
exact  calculation. 

The  material  of  the  boiler,  as  will  be  shown  later,  should  be 
tough  and  ductile  iron,  or,  better,  a  soft  steel  containing  only  suffi- 
cient carbon  to  insure  melting  in  the  crucible  or  on  the  hearth 
of  the  melting-furnace,  and  so  little  that  no  danger  may  exist 
of  hardening  and  cracking  under  the  action  of  sudden  and  great 
changes  of  temperature. 


14  THE   STEAM-BOILER. 

Where  iron  is  used  it  is  necessary  to  select  a  somewhat 
hard  but  homogeneous  and  tough  quality  for  the  firebox 
sheets  or  any  part  exposed  to  flames. 

The  factor  of  safety  is  very  often  too  low.  The  boiler 
should  be  built  strong  enough  to  bear  a  pressure  at  least  six 
times  the  proposed  working-pressure  ;  as  the  boiler  grows  weak 
with  age,  it  should  be  occasionally  tested  to  a  pressure  far 
above  the  working-pressure,  which  latter  should  be  reduced 
gradually  to  keep  within  the  bounds  of  safety.  The  factor  of 
safety  is  seldom  more  than  four  in  new  boilers;  and  even  this 
is  reduced  practically  by  the  operation  of  the  inspection  laws. 

Effective  development  of  heat  is  secured  primarily  by  the 
selection  of  good  fuel,  by  which  is  usually  meant  fuel  which 
consists,  to  the  greatest  possible  extent,  of  available  combusti- 
ble material ;  but  for  the  purposes  of  the  engineer  who  designs 
the  boiler,  or  of  the  owner  for  whom  it  is  to  be  constructed,  the 
real  criterion  of  quality  is  the  quantity  of  heat  which  the  com- 
bustible, as  burned  in  the  furnace,  will  yield  for  any  given  sum 
of  money  expended  in  obtaining  that  heat.  The  cost  of  a  fuel 
to  the  consumer  consists,  not  simply  of  money  paid  for  it  to 
the  dealer  who  supplies  it,  but  also  of  cost  of  transportation 
and  of  placing  in  the  grate,  of  removal  of  ash,  of  incidental  ex- 
penses inseparable  from  its  use,  such  as  injury  to  boilers  and 
other  property,  increased  risks,  and  other  such  expenses,  many 
if  not  most  of  which  are  very  difficult  of  determination  with 
any  satisfactory  decree  of  accuracy.  Other  things  being  equal, 
that  fuel  which  gives  the  greatest  quantity  of  available  heat  for 
the  total  money  expenditure  is  that  which  permits  most  effec- 
tive development  in  the  sense  here  taken.  Effective  heat-de- 
velopment from  any  selected  fuel  is  secured,  as  already  stated, 
by  its  complete  combustion  in  such  manner  as  to  give  the 
highest  possible  temperature. 

Effective  transfer  of  heat  is  secured  by  such  a  form  of 
steam-generator,  and  such  extent  and  disposition  of  "  heating- 
surfaces,"  as  will  most  completely  utilize  the  heat  developed  in 
the  furnace  and  flues  by  causing  it  to  flow,  with  the  least  pos- 
sible loss,  into  the  water  and  steam  contained  within  the  boiler ; 
and  this  is  effected  by  proper  arrangement  of  surfaces  absorb- 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.      15 

ing  heat  from  the  gases  and  yielding  it  to  the  liquid  as  already 
generally  described. 

Effective  storage  of  heat  can  be  secured  by  providing  large 
volumes  of  water  and  of  steam,  within  which  the  heat  transferred 
from  the  furnace  and  flues  can  be  stored,  and  by  carefully  pro- 
tecting the  whole  heated  system  from  waste  by  conduction  or 
radiation  to  adjacent  bodies.  Where  the  demand  is  steady,  and 
the  supply  from  the  fuel  fairly  steady  also,  the  amount  stored 
need  not  be  great,  as  the  use  of  the  reservoir  is  simply  that  of 
a  regulator  between  furnace  and  engine  or  other  apparatus  re- 
ceiving it ;  but  where  either  supply  or  demand  is  variable,  con- 
siderable storage  capacity  may  be  needed. 

8.  Efficient  Utilization  of  Heat  is  as  essential  to  the  satis- 
factory working  of  any  system  of  generation  and  application  of 
heat  as  is  efficient  production,  transfer,  and  storage.  The  mode 
of  attaining  maximum  efficiency  depends  upon  the  nature  of 
the  demand  and  the  method  of  expenditure  ;  and  the  considera- 
tion of  this  subject  in  detail  would  be  here  out  of  place.  In 
general  it  may  be  said  that  where  the  heat  and  steam  are  re- 
quired for  the  impulsion  of  an  engine,  the  higher  the  safe  pres- 
sure and  the  practically  attainable  temperature  at  which  the 
supply  is  effected,  the  more  efficient  the  utilization  of  the  heat. 
These  limits  of  temperature  and  pressure  are  the  higher  as  the 
actual  working  conditions  are  made  the  more  closely  to  approxi- 
mate to  the  ideal  conditions  prescribed  by  pure  science. 

Where  heating  simply,  without  transformation  into  work,  is 
intended,  the  principal  and  only  very  important  requisite, 
usually,  is  to  provide  such  thorough  protection  for  the  system 
of  transfer  and  use,  that  no  wastes  of  importance  can  take  place 
by  radiation  or  conduction.  The  character  of  the  steam  made, 
as  to  humidity,  is  in  this  case  comparatively  unimportant ;  but 
in  the  preceding  case  it  will  be  found  essential  that  it  should  be 
always  dry,  and  it  is  often  much  the  better  for  being  super- 
heated considerably  above  the  boiling-point  due  to  its  pressure. 

The  actual  standing  of  the  best  steam-engine  of  the  present 
time,  as  an  efficient  heat-engine,  is  really  very  high.  The 
sources  of  loss  are  principally  quite  apart  from  the  principles  of 
design  and  construction,  and  even  from  the  operation  of  the 


1 6  THE   STEAM-BOILER. 

machine ;  and  it  may  be  readily  shown  that,  to  secure  any  really 
important  advance  toward  theoretical  efficiency,  a  radical  change 
of  our  methods  must  be  adopted,  and  probably  that  we  must 
throw  aside  the  heat-engine  in  all  its  forms,  and  substitute  for 
it  some  other  apparatus  by  which  we  may  utilize  some  mode  of 
motion  and  of  natural  energy  other  than  heat. 

The  very  best  classes  of  modern  steam-engines  very  seldom 
consume  less  than  two  pounds  (0.9  kilog.)  of  coal  per  horse- 
power per  hour,  and  it  is  a  good  engine  that  works  regularly 
on  three  pounds  (1.37  kilog.). 

The  first-class  steam-engine,  therefore,  yields  less  than  10 
per  cent  of  the  work  stored  up  in  good  fuel,  and  the  average 
engine  probably  utilizes  less  than  5  per  cent.  A  part  of  this 
loss  is  unavoidable,  being  due  to  natural  conditions  beyond  the 
control  of  human  power,  while  another  portion  is,  to  a  consid- 
erable extent,  controllable  by  the  engineer  or  by  the  engine- 
driver.  Scientific  research  has  shown  that  the  proportion  of 
heat  stored  up  in  any  fluid,  which  may  be  utilized  by  perfect 
mechanism,  must  be  represented  by  a  fraction,  the  numerator 
of  which  is  the  range  of  temperature  of  the  fluid  while  doing 
useful  work,  and  the  denominator  of  which  is  the  temperature 
of  the  fluid  when  entering  the  machine,  measured  from  the 
"  absolute  zero." 

Thus,  steam,  at  a  temperature  of  320°  Fahr.,  being  taken 
into  a  perfect  steam-engine,  and  doing  work  there  until  it 
is  thrown  into  the  condenser  at  100°  Fahr.,  would  yield 

•5  O/~\    T  (*"V~) 

: — -y-  —  °-2%  +>  or  rather  more  than    one  fourth    of   the 

320  -\-  461 

work  which  it  should  have  received  from  each  pound  of  fuel. 
The  proportion  of  work  that  a  non-condensing  but  other- 
wise perfect  engine,  using  steam  of  75  pounds  (5  atmos.)  pres- 
sure, could  utilize  would  be- —  =0.14  —  4;  and,  while 

320  +  461 

the  perfect  condensing  engine  would  consume  two  thirds  of  a 
pound  (0.3  kilog.)  of  good  coal  per  hour,  the  perfect  non-con- 
densing engine  would  use  i^  pounds  (0.6  kilog.)  per  hour  for 
each  horse-power  developed,  the  steam  being  taken  into  the 
engine  and  exhausted  at  the  temperatures  assumed  above. 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.      I/ 

Also,  were  it  possible  to  work  steam  down  to  the  absolute  zero 
of  temperature,  the  perfect  engine  would  require  but  0.19 
pound  (0.09  kilog.)  of  similar  fuel. 

It  may  therefore  be  stated,  with  a  close  approximation  to 
exactness,  that  of  all  the  heat  derived  from  the  fuel  about 
seven  tenths  is  lost  through  the  existence  of  natural  conditions 
over  which  man  can  probably  never  expect  to  obtain  control, 
two  tenths  are  lost  through  imperfections  in  our  apparatus,  and 
only  one  tenth  is  utilized  in  even  good  engines.  Boiler  and 
engine  are  intended  to  be  included  when  writing  of  the  steam- 
engine  above.  In  this  combination  a  waste  of  probably  two 
tenths  at  least  of  the  heat  derived  from  the  fuel  takes  place  in 
the  boiler  and  steam-pipes,  on  the  average,  in  the  best  of  prac- 
tice, and  we  are  therefore  only  able  to  anticipate  a  possible 
saving  of  0.2  X  0.75  =  0.15,  about  one  sixth  of  the  fuel  now 
expended  in  our  best  class  of  engines,  by  improvements  in  the 
machine  itself.  The  best  steam-engine,  apart  from  its  boiler, 
therefore,  has  0.85,  about  five  sixths,  of  the  efficiency  of  a  perfect 
engine,  and  the  remaining  sixth  is  lost  through  waste  of  heat 
by  radiation  and  conduction  externally,  by  condensation  within 
the  cylinder,  and  by  friction  and  other  useless  work  done  within 
itself.  It  is  to  improvement  in  these  points  that  inventors  must 
turn  their  attention  if  they  would  improve  upon  the  best  modern 
practice  by  changes  in  construction. 

To  attain  further  economy,  after  having  perfected  the 
machine  in  these  particulars,  they  must  contrive  to  use  a  fluid 
which  they  may  work  through  a  wider  range  of  temperature,  as 
has  been  attempted  in  air-engines  by  raising  the  upper  limit  of 
temperature,  and  in  binary  vapor  engines  by  reaching  toward  a 
lower  limit,  or  by  working  a  fluid  from  a  higher  temperature 
than  is  now  done  down  to  the  lowest  possible  temperature. 
The  upper  limit  is  fixed  by  the  heat-resisting  power  of  our 
materials  of  construction,  and  the  lower  by  the  mean  tempera- 
ture of  objects  on  the  surface  of  earth,  being  much  lower  at 
some  seasons  than  at  others.  In  the  boiler  the  endeavor  must 
be  made  to  take  up  all  the  heat  of  combustion,  sending  the 
gases  into  the  chimney  at  as  low  a  temperature  as  possible,  and 
securing  in  the  furnace  perfect  combustion  without  excess  of 


1 8  THE   STEAM-BOILER. 

air-supply.     The  best  engines  still  lack   1 5   per  cent  of  perfec- 
tion, and  the  best  boilers,  as  an  average,  over  30  per  cent. 

9.  Safety  in  Operation  is  one  of  the  most  essential  require- 
ments which  the  designer,  constructor,  and  user  of  steam-boilers 
must  be  prepared  to  fulfil.     As  will  be  seen  later,  the  quantity 
of  stored  heat-energy  in  the  steam-boiler  is  usually  enormous, 
and  this  energy  is  stored  under  such  conditions  that,  if  set  free 
by  the  rupture   of  the  containing  vessel,  wide-spread  disaster 
may  ensue.     This  stored  energy  is  at  all  times  ready  to  instantly 
assume  the  kinetic  form  when  permitted,  and  by  doing  mechani- 
cal work  on  all  adjacent  objects,  to  produce  most  extraordinary 
effects ;  it  is  stored  energy  of  the  most  perfectly  elastic  kind,  as 
well  as  of  high  tension.     The  most  absolutely  reliable  means 
known  to  the  engineer  must  be  adopted  for  the  safe  and  per- 
manent control  of  such  magazines  of  latent  power. 

Those  methods  of  securing  safety  which  have  been  found 
most  satisfactory  have  been — 

(1)  The  division  of  the    confined  energy   among  compara- 
tively small  masses  of  steam  and  water  contained  in  correspond- 
ingly small  communicating  chambers,  so  constructed  that  the 
rupture  of  one  will  be  unlikely  to  produce  fracture  of  any  other. 

(2)  The  adoption  of  the  very  best  material  and  of  the  best 
possible  construction,  and  so  proportioning  all  parts  exposed  to 
stress  and   strain    that    they  may  withstand  pressures    several 
times  as  great  as  the  maximum  intended  to  be  carried. 

(3)  Careful  and  intelligent  operation  and  preservation. 

10.  The    Appurtenances     or    Accessories    of    Steam- 
boilers   are  those  attached   parts  and  apparatus  which,  while 
not,  strictly  speaking,  actually  essential  elements  of  the  struc- 
ture specially  designated  as  the  boiler,  are  nevertheless  essen- 
tial to  its  safe  and  economical  operation :  such  as,  for  example, 
safety   and    other   valves,    gauge-cocks,    feed-pumps,    dampers, 
grates,  and  "  settings." 

Safety-valves  are  automatically  self-operating  apparatus 
which  open  and  permit  the  steam  to  issue  from  the  boiler 
whenever  the  pressure  reaches  a  limit  at  which  they  are  ar- 
ranged to  act.  Steam-valves  are  the  valves,  usually  operated 
by  screws,  which,  when  open,  permit  the  steam  to  leave  the 
boiler  and  pass  away  through  the  steam-pipes.  Stop-valves  are  a 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.      19 

variety  of  valve  which  may  be  used  to  stop  the  passage  of  steam 
from  the  boiler:  they  may  be  "screw  stop-valves,"  or  simple 
valves  moved  directly  by  hand.  Check-valves,  commonly  in- 
troduced at  the  junction  of  the  feed-water  supply-pipe  with 
the  boiler,  are  so  arranged  as  to  open  automatically  when  the 
stream  enters,  but  to  close  against  a  return  current :  they  are 
sometimes  pinned  to  their  seats,  when  desirable,  by  a  screw,  in 
which  case  they  are  called  "  screw-checks."  Gauge-cocks  are 
set  at,  and  above  or  below,  the  intended  working  water-level 
of  the  boiler,  and,  when  opened,  by  discharging  steam  or  water, 
indicate  the  actual  position  of  the  water-line.  Glass  water- 
gauges  are  glass  tubes  set  in  such  manner  that  the  water 
stands  in  a  vertical  tube  at  the  same  height  as  the  water  in  the 
boiler,  the  top  of  the  glass  communicating  with  the  steam- 
space,  and  the  lower  end  with  the  water-space  of  the  boiler. 

II.  The  Classification  of  Steam-boilers  may  be  based 
upon  either  a  comparison  of  their  forms  or  of  their  purpose. 
Under  the  former  we  have  the  plain  cylindrical,  the  flue,  the 
tubular,  or  the  sectional  boiler;  under  the  latter,  stationary, 
locomotive,  or  marine  boilers.  For  the  purposes  of  this  work, 
the  following  may  be  taken  as  a  satisfactory  scheme : 

Plain  cylindrical  boilers. 
Cornish  or  single-flue. 
Lancashire  or  two-flue. 

Stationary  •{   Multin<ue  and  return-flue  boilers. 

Cylindrical  fire-tube  boilers. 
Firebox  boilers. 
Sectional  boilers. 
Peculiar  forms. 
i  Common  type. 

Locomotive  .     .     .  j  Wooton  boilers. 
(  Special  devices. 

/  Flue. 
Older  types  •<  Flue  and  tube. 

Marine  .  J  '  Tubular. 

Scotch  or  drum  boilers. 
Water-tube  and  sectional. 
Miscellaneous  forms. 


2O  THE   STEAM-BOILER. 

12.  The  Modern  Standard  Types  of  Boiler  are  becom- 
ing  rapidly  settled  in    a    few  well-defined    forms  which   have 
been  found  to  be  most  satisfactory,  all  things  considered,  each 
in  its  own  special  province.     These  are  specified  in  the  list  just 
presented.     But  many  boilers  have  become  so  thoroughly  well 
adapted   to   the    special   work  to  which  they  are    customarily 
applied  as  to    have    almost  or  quite  entirely  displaced    other 
forms,  which  in  turn  are  as  generally  adopted  for  other  uses. 
Thus,  where  the  feed-water  supplied  to  land  boilers,  in  locali- 
ties where  fuel  is  cheap,  or  water  bad,  and  certain  to  produce 
serious  incrustation,  the  plain  cylindrical  boiler  is  almost  univer- 
sally employed ;    where  the  fuel  is  costly  and  the    feed-water 
pure,  the  tubular  boiler  is  as  universally  adopted  ;  while  inter- 
mediate conditions  lead  to  the  use  of  intermediate  forms.    The 
locomotive  boiler  is  standard    for  its  place  and  purpose,  and 
no    other   form  has    ever  yet    competed    with    it  in    thorough 
adaptation  to  that  peculiar  case.     The  high  pressures  carried 
and  the  necessity  of  great  economy  at  sea  have  made  the  so- 
called  "  Scotch"  or  "  drum"    boiler   standard    in  trans-oceanic 
steam  navigation.     Where  small  area  of  floor-space  and  ample 
"  head-room"  are  found,  the  upright  cylindrical  tubular  boiler 
is  the  standard  form  ;  if  the  head-room  is  less  and  the   floor- 
space  larger,  a  modification  of  the  locomotive  type  finds  appli- 
cation for  stationary  purposes. 

13.  Mixed  Types  of  boiler  are  often  constructed  for  special 
purposes  or  experimentally.     In  the  shallow-water  navigation 
of  the  United   States  of  America,  as   on   the   Hudson   River, 
the  flue  and  tube  boiler  is  much  used  ;  the  locomotive  type  of 
boiler,  with  fewer  and  larger  tubes  than  are  adopted  in  locomo- 
tive practice,  has  often  found  use  in  stationary  practice.     New 
designs  are  continually  coming  forward  which  illustrate  such 
forms  of  boiler.     As  a  rule,  however,  they  are  not  found  pref- 
erable to  the  simpler  and  standard  types. 

14.  Mixed  Applications  are  sometimes  required,  as  where 
the  same  boiler  supplies  steam  for  power  and  for  heating  pur- 
poses.    In  this  case  the  pressure  carried  on  the  boiler  is  fixed 
at  the  proposed  maximum  for  the  engine,  and  the  lower  pres- 
sures required  for  the  other   purpose  are  secured  by  the  use 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.     21 

of  a  "  reducing"  or  "  pressure-reducing"  valve.  The  steam- 
heating  systems  of  cities  often  illustrate  this  case,  furnishing 
steam,  as  they  do,  for  heating  buildings,  for  cooking,  and  to 
steam-engines  at  all  parts  of  the  area  covered  by  them. 

15.  Common  Forms  of  "  Shell "  Boilers,  as  those  boilers 
are  called  in  which  the  structure  consists  of  an  external  case 
enclosing  steam  and  water,  flues  and  tubes,  are  the  following : 

(i)  The  Plain  Cylindrical  Boiler  consists,  as  shown  in  section 
(Fig.  15),  and  in  front  elevation  (Fig.  16),  of  a  simple  cylin- 


FIG.  15. — SECTION  OF  CYLINDRICAL  BOILER. 

drical  vessel,  A,  made  of  boiler-plate,  fitted  with  heads  at  each 
end,  B,  B ;  which  heads  are  sometimes  of  sheet-iron  and  some- 
times of  cast-iron.  A  steam-dome,  C,  on  the  upper  side, 
usually  serves  as  a  collector  and  reservoir  for  the  steam,  as  it 
rises  from  the  water  into  the  steam-space,  and  serves  also  as 
the  point  of  attachment  for  the  steam-pipe,  D  D,  and  safety- 
valve,  E  E,  both  of  which  thus  take  steam  from  the  highest 
and  driest  part  of  the  interior  of  the  boiler. 

The  fire  is  built  in  the  detached  furnace,  F  F,  the  products 
of  combustion  passing  under  the  boiler  to  the  rear,  at  G,  where 


22 


THE   STEAM-BOILER. 


a  flue  leads  off  to  the  chimney.  The  "  setting"  consists  of 
side-walls  and  ends,  H  H,  of  brick,  and  a  covering,  /  /,  which 
is  often  merely  a  filling  of  ashes  or  other  non-conductor,  or  an 
arch  of  brickwork  carried  over  from  the  side-walls.  "  Binders," 
K  K,  and  rods,  L  L,  tie  the  whole  together,  and  resist  any 
change  of  form  due  to  variations  of  temperature.  The  grates, 


FIG.  16.— FRONT  OF  CYLINDRICAL  BOILER  AND  SETTING. 

M  Mt  are  supported  at  the  rear  by  the  bridge-wall,  N  N,  of 
which  the  upper  part  is  usually  built  of  fire-brick.  The  rear 
end  of  the  boiler  is  often  carried  on  rollers,  to  prevent  danger  of 
injury  with  the  changes  of  form  due  to  variations  of  tempera- 
ture such  as  are  produced  by  the  introduction  of  cold  feed- 
water. 

(2)  The  Cylindrical  Flue  Boiler  (Fig.  17)  is  a  plain  cylinder, 
like  the  preceding  form,  but  with  one  or  more  flues  passing 
through  it  from  end  to  end.  The  setting  is  usually  quite 
similar  to  that  of  the  plain  cylinder,  except  as  necessarily 
modified  to  meet  the  requirements  of  the  flue.  The  shell  is 
generally  shorter  than  that  of  the  first-described  boiler,  the 
heating-surface  considerably  greater. 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.     2$ 

(3)   The  Cylindrical  Tubular  Boiler  is  shown  in  one  of  the 
best    forms  in    Fig.   1 8.     It  consists  of  a  cylindrical  shell  con- 


FIG.  17.— CYLINDRICAL  FLUE  BOILER. 


structed  much  as  in  Fig.  15,  with  a  set  of  tubes  carried  from 
end  to  end,  and  set  as  closely  as  is  practicable  without  inter- 
fering too  seriously  with  the  circulation  of  the  water  within  it. 


FIG.  18. — CYLINDRICAL  TUBULAR  TOILER. 


The  peculiar  feature  of  the  illustration  is  the  introduction  of 
the  very  large  single  sheet  which  is  seen  to  make  the  whole 
lower  two  thirds  or  more  of  the  shell ;  this  construction  pre- 


THE   STEAM-BOILER. 


venting  the  fire  reaching  seams  and  riveting,  as  occurs  in  the 
usual  construction. 


FIG.  19. — CYLINDRICAL  TUBULAR  BOILER  AND  SETTING. 

The   setting  of  this  kind  of  boiler  is  shown  in  Figs.  19  and 
20.     The  weight  of  the  boiler  is  here  taken  by  "  lugs"  on  each 

side  and  by  them  transferred  to  the 
brickwork  of  the  setting.  In  other 
cases  the  boiler  is  suspended  from 
girders  crossing  the  structure  later- 
ally ;  and  the  suspension-rods  carry- 
ing the  boiler  are  sometimes  allowed 
vertical  play,  under  the  action  of 
expansion  and  contraction  of  the 
whole  system,  by  the  introduction 
of  springs  of  rubber  or  steel,  thus 
permitting  very  uniform  distribu- 
tion of  the  weight  at  all  times.  In 
many  cases  the  gases,  instead  of 
being;  carried  over  the  boiler  to  the 

TIG.  20. — SECTION  OF  TUBULAR  BOILER 

AND  SETTING.  chimney,  as  shown  in   Fig.   19,  are 

taken  directly  to  the  chimney  from  the  front  of  the  boiler,  as 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.      2$ 


in  Fig.  1 6.  It  is  not  always  thought  safe  to  expose  the  top 
and  steam  spaces  of  the  boiler  to  the  heat  of  the  escaping 
gases ;  but  the  practice  is  not  an  uncommon  one,  even  with 
reputable  builders.  The  air-spaces  in  Fig.  20,  at  either  side 
in  the  walls  of  the  setting,  give  an  additional  protection  from 
loss  of  heat,  and  a  certain  amount  of  elasticity  of  setting.  This 
is  the  most  common  of  all  forms  of  steam-boiler. 


FIG.  21. — FIKEBOX  TUBULAR  BOILER. 

(4)  The  Firebox  Flue  Boiler  is  so  made  in  order  that 
the  whole  may  become  "self-contained,"  and  brickwork  dis- 
pensed with.  Adding  the  firebox  to  the  tubular  (Fig.  21), 
forms  the  locomotive  type  of 
boiler.  In  stationary  boilers, 
however,  the  tubes  are,  as  a 
rule,  larger  and  less  numerous 
than  in  the  locomotive  boiler. 
These  boilers  require  no  set- 
ting or  connections  other  than 
the  parts  needed  to  connect 
them  with  the  chimney-flue. 

This  arrangement  is  seen  in  Fig.  22.     The  advantages  of  this 
type  are  the  low  cost  of  installation,  the  more  complete  ac- 


26 


THE   STEAM-BOILER. 


cessibility  of  the  exterior  for  inspection  and  repair,  the  reduc- 
tion of  floor-space  occupied,  and  the  portability  of  the  boiler. 


FIG.  23.— THE  UPRIGHT  BOILER. 


FIG.  24.— UPRIGHT  TUBULAR 
BOILER. 


(5)   The  Upright  Boiler  is  usually  a  firebox  tubular  boiler, 
designed  to  stand  vertically,  as  in  Fig.  23,  and  to  occupy  mini- 


FIG.  25.— BATTERY  OF   BOILERS. 

The  above  cut  represents  a  pair  of  Cornish  boilers  set  in  brick-work,  connected  so  as  to  be 
worked  either  together  or  separately. 

mum  floor-space.    Its  construction  at  the  upper  end  is  often  such 
as  to  permit  the  upper  extremities  of  the  tubes  to  be  kept  be- 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.     2J 


low  the  water-line.  In  many  cases,  however,  the  tubes  are  car- 
ried directly  through  to  the  upper  head,  as  is  seen  in  Fig.  24. 
This  figure  also  exhibits  the  method  of  attaching  gauges  and 
safety-valves.  This  boiler  is  much  used  where  it  is  important 
to  save  floor-space,  and  where  head-room  can  be  obtained.  It 
is  the  usual  form  in  steam  fire-engines. 

16.  A  "Battery"  of  Boilers  (Fig.  25) 
consists  of  two  or  more,  placed  side  by  side, 
the  total  power  demanded  being  greater  than 
it  is  considered  advisable  to  construct  a  single 
boiler  to  supply.  In  such  cases  it  is  usually 
important  that  they  should  be  so  set  and  con- 
nected that  either  or  any  of  them  may  be 
operated  separately.  To  secure  this  resultr 
the  connections  with  the  feed  and  steam-pipes 
must  be  so  made  that  it  may  be  perfectly 
practicable  to  put  the  feed  on  either  or  any 
FIG  26  -UPRIGHT  BOILER  of  the  boilers  in  the  battery,  and  to  take  steam 

WITH  F.ELU  TUBES.        frQm    dther    Qr 


own  separate  safety-valve,  check-valve,  and  steam-gauge. 

An  upright  boiler  fitted  with  "  Field  tubes  "  is  shown  in  Fig. 
26.  The  internal,  cir- 
culating, tubes  project 
slightly  above  the 
crown-sheet,  and  are 
carried  down  inside  the 
main  tube,  nearly  to 
the  closed  lower  end. 
The  water  enters  the 
centre  tube,  flows  out 
at  its  lower  end,  and 

rises  in  the  outer  tube  FIG.  27.-LocoMOTivE  BOILER. 

—  on  all  sides  the  smaller  one  —  issuing  above  the  crown-sheet  into 
the  general  body  of  water,  and  there  discharging  the  accompany- 
ing steam  which  had  been  made  during  the  period  of  circulation. 

17.  The  Locomotive  Boiler  is  always  given  a  form  sub- 
stantially as  represented  in  Fig.  27,  and  consists  of  a  firebox 
of  rectangular  form,  attached  to  a  cylindrical  shell  closely  filled 


28 


THE  STEAM-BOILER. 


with  fire-tubes,  through  which  the  gases  pass  directly  to  the 
smoke-stack.  Strength,  compactness,  great  steaming  capacity, 
fair  economy,  moderate  cost,  and  convenience  of  combination 
with  the  running  parts,  are  secured  by  the  adoption  of  this 
form.  It  is  frequently  used  also  for  portable  and  stationary 
engines.  It  was  invented  in  France  by  M.  Seguin,  and  in 
England  by  Booth,  and  used  by  George  Stephenson  at  about 
the  same  time — 1828  or  1829. 


FIG.  28.— THE  LOCOMOTIVE.    Section. 

This  form  of  steam-boiler  has  been  found  to  lend  itself  with 
peculiar  handiness  to  the  special  requirements  of  locomotive 
construction,  and  its  use  is  universal  for  this  purpose.  . 

18.  The  "Marine"  Boilers  are  often  of  very  different 
form  from  those  used  on  land.  They  have  assumed  their 
present  forms  after  many  years  of  experience  and  slow  adapta- 
tion to  the  special  conditions  by  which  they  are  controlled. 
When  steam-pressures  were  customarily  low,  the  controlling 
condition  was  the  form  of  the  vessel,  and  boilers  were  given 
such  shapes  as  would  permit  of  their  being  compactly  stowed 
on  board  ship ;  in  the  later  days  of  very  high  pressure  which 
have  followed  the  introduction  of  the  surface-condenser,  and 
of  high  expansion,  the  form  of  the  steam-generator  is  deter- 
mined mainly  by  the  demand  for  their  safe  operation. 

Fig.  29  shows  one  of  the  types  of  boiler  in  most  common 
use  on  the  steamers  generally  seen  on  the  Eastern  American 
rivers,  and  on  the  coast,  before  the  period  of  high  steam  and 
great  economy  had  -opened. 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE,     29 

It  is  known  as  the  "  Return-flue"  boiler,  the  flame  and 
gases  from  the  furnace  passing  back  to  the  "  back-connection" 
through  one  set  of  flues,  usually  of  10  to  20  or  even  24  inches 
in  diameter,  and  thence  to  the  "  front-connection"  over  the 
furnace,  and  to  the  "  uptake,"  and  chimney  or  "  smokestack," 
by  a  set  of  flues  of,  as  a  rule,  smaller  size  and  larger  number. 
This  is  seen  to  be  a  "  firebox  boiler,  no  brickwork  setting  being 
admissible  on  shipboard. 


FIG.  29.— FLUES  AND  RETURN-TUBES. 


Surrounding  the  chimney  uptake  is  a  reservoir,  called  the 
"  steam-chimney,"  which  answers  the  double  purpose  of  a 
steam-dome  and  a  drier,  or  "  superheater,"  in  which  the  steam 
may  part  with  its  suspended  water,  and  often  become  heated 
above  the  temperature  of  saturation  by  the  heat  from  the 
chimney  gases.  An  elaborate  system  of  bracing  and  staying 
is  required  for  a  boiler  of  this  type.  The  sketch  (Fig.  29) 
shows  one  of  a  pair  of  boilers  arranged  to  discharge  their  flue 
gases  into  a  common  chimney. 

An  effort  to  secure  increased  steaming  capacity  and 
economy  in  this  boiler  resulted  in  the  production  of  the  boiler 


30  THE   STEAM-BOILER. 

with  direct  flues  and  return-tubes,  the  latter  being  usually  from 
three  to  five  inches  in  diameter.  This  represents  the  later 
type,  and  one  which  is  still  very  often  used  on  paddle-steamers 
on  Long  Island  Sound  and  on  the  rivers  connected  with  that 
system  of  water  communication. 

Fig.  30  illustrates  a  still  more 
advanced  type,  the  marine  tubular 
boiler,  extensively  used  in  naval 
and  other  sea-going  steamers,  car- 
rying from  twenty-five  to  forty 
pounds  steam-pressure.  The  fur- 
nace discharges  its  gases  directly 
into  the  back-connection,  whence 
they  pass  forward  into  the  front 
connection  and  stack  through  a 
set  of  tubes,  which  are  commonly 

22  to  3^  inches  in  diameter.  This  arrangement  gives  a 
very  compact,  well-proportioned  boiler,  comparatively  easy 
of  calculation  and  construction,  and  especially  convenient  in 
bracing  and  staying.  Several  furnaces  can  in  this  boiler  be 
conveniently  placed  side  by  side  and  connected  to  a  common 
uptake. 

19.  The  Marine  Water-tube  Boiler  (Fig.  31)  represents 
a  type  which  has  been  often  proposed  for  use  at  sea,  but  which 
has  never  succeeded  in  finding  its  way  into  common  use. 


FIG.  30.— MARINE  TUBULAR  BOILER. 


FIG.  31.— MARINE  WATER-TUBE  BOILER. 


Lord  Dundonald  in  Great  Britain  and  James  Montgomery 
in   the    United    States   introduced    boilers   of   the  water-tube 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.     31 

type  before  the  middle  of  the  century,  and  the  form  here  il- 
lustrated, as  originally  designed  by  Mr.  Martin  of  the  U.  S. 
Navy,  was  very  extensively  employed  on  the  vessels  of  the 
navy  during  the  Civil  War.  In  these  boilers  the  gases  pass 
from  the  back-connection  to  the  front  through  a  "  tube-box" 
placed  in  the  water-space  of  the  boiler,  which  tube-box  con- 
tains a  large  number  of  vertical  tubes  within  which  the  water 
circulates  from  the  lower  to  the  upper  side,  while  the  gases 
pass  among  and  around  the  tubes. 

These  boilers  were  found  by  Isherwood  to  give  a  somewhat 
larger  steaming  capacity  and  greater  economy  also  than  the 
corresponding  boiler  of  the  fire-tube  type;  but  the  difficulty 
of  repairing  leaky  tubes  and  incidental  disadvantages,  as  well 
as  their  greater  cost,  prevented  their  permanent  adoption  in 
either  the  navy  or  the  merchant  service. 

20.  The  Scotch  or  Drum  Boiler  (Fig.  32)  is  the  outcome 
of  the  attempt  to  secure  a  safe  form  of  boiler  for  high  pres- 


FIG.  32.— SCOTCH  OR  DRUM  BOILER. 


sures,  and  it  has,  very  naturally,  assumed  the  cylindrical  form 
of  shell,  while  retaining  the  general  disposition  of  furnace  and 
tubes  illustrated  in  the  last-described  fire-tube  boiler.  The 
furnaces  are  large,  set  in  very  thick  flues ;  the  grates  are  set  in 
them  at  very  nearly  the  horizontal  diametrical  line,  and,  in  the 
case  illustrated,  the  boiler  is  "  double-ended."  Heavy  stay- 
rods,  connecting  the  two  ends,  make  the  heads  capable  of 
safely  carrying  their  enormous  loads.  These  boilers  often 
carry  100  and  150  pounds  pressure,  and  sometimes  even  more, 


32  THE   STEAM-BOILER. 

and  are  built  of  between  10  and  20  feet  diameter,  and  of  iron 
or  steel  from  f  to  i^  inches  in  thickness. 

Fig.  33  exhibits  the  method  of  setting  and  of  connection 
of  these  boilers,  as  customarily  practised  where  "  single-ended," 
i.e.,  with  the  furnaces  at  one  end  only,  as  here  seen.  Either 
or  any  of  these  boilers,  as  so  set,  may  be  used  or  repaired  sep- 
arately if  necessary. 

For  small  powers  these  boilers  are  often  given  the  form  and 
structure  shown  in  Fig.  3ty  which  represents  a  boiler  designed 
for  a  small  yacht  or  a  torpedo-boat ;  it  is  three  or  four  feet  in 


FIG.  33.— SETTING  AND  CONNECTION  OF  SCOTCH  BOILERS. 

diameter  and  four  to  six  feet  long,  and  is  calculated  for  from 
five  to  ten  or  twelve  horse-power. 

21.  Sectional  Boilers  are  all  constructed  to  meet  the  con- 
ditions and  requirements  so  well  stated  by  Col.  Stevens  in  his 
specification  for  his  British  patent  of  1805,  in  which  he  says 
that,  to  derive  advantage  from  his  principle,  "  it  is  absolutely 
necessary  that  the  vessel  or  vessels  for  generating  steam  should 
have  strength  sufficient  to  withstand  the  great  pressure  from  an 
increase  of  elasticity  in  the  steam ;  but  this  [total]  pressure  is 
increased  or  diminished  in  proportion  to  the  capacity  of  the 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE.     33 

containing  vessel.  The  principle,  then,  of  this  invention  con- 
sists in  forming  a  boiler  by  means  of  a  system  or  combination 
of  a  number  of  small  vessels,  instead  of  using,  as  in  the  usual 
mode,  one  large  one ;  the  relative  strength  of  the  materials  of 
which  these  vessels  are  composed  increasing  in  proportion  to 
the  diminution  in  capacity." 


FIG.  34. — MARINE  BOILER  OF  SMALL  POWER. 

Stevens'  boilers  were  of  two  kinds:  the  one  that  shown  in 
Fig.  10 ;  the  other,  and  that  specifically  shown  in  the  patent, 
consisting  of  systems  of  small  tubes  grouped  in  circular  con- 
centric rows,  and  connected  at  each  end  by  annular  heads  and 
chambers  of  sufficiently  small  capacity  to  be  safe,  while  still 
large  enough  to  permit  good  circulation. 

The  boiler  adopted  in  Gurney's  steam-carriage  (Fig.  1 1)  is  a 
later  type,  which  has  been  more  than  once  since  reproduced ; 
and  nearly  all  recent,  familiar,  forms  of  the  sectional  boiler  are 

3 


34 


THE   STEAM-BOILER. 


constructed  of  systems  of  tubes  united  at  the  ends,  and  with 
the  feed-apparatus,  steam-drum,  and  mud-drum,  by  what  are 
known  as  "  headers,"  through  which  the  general  circulation  is 
secured.  In  some  cases  the  boiler  has  been  made  wholly  or 
partly  of  cast-iron,  as  the  early  Babcock  &  Wilcox  (Fig.  35), 
which  consisted  of  a  system  of  horizontal  cast-iron  tubes  serv- 
ing both  as  water  connections  and 
as  steam-chambers,  and  a  second 
system  of  tubes  set  at  a  considera- 
ble inclination  from  the  horizontal, 
the  two  sets  united  by  headers. 

The  Babcock  &  Wilcox  Boiler, 
in  the  latest  and  best  form,  how- 
ever (Fig.  36),  is  wholly  of  wrought- 
iron  or  steel.  The  same  general 
arrangement  of  tubes  is  preserved ; 

FIG.  35.— CAST-IRON  SECTIONAL  BOILER.    .  r      , 

but  the  upper  part  of  the  construc- 
tion consists  of  one  or  more  steam  and  water  drums  of  com- 
paratively large  diameter.  These  are  away  from  the  fire,  and 
cannot  be  reached  by  the  gases  until  they  are  cooled  down  to 
a  safe  temperature  by  passing  through  the  lower  system  of 


FIG.  36.— BABCOCK  &  WILCOX  BOILER. 


heating  surfaces,  the  inclined  tubes.  The  water-line  in  the 
drum  is  carried  at  about  its  middle,  and  a  dry-pipe,  seen  at  the 
top,  carries  off  the  steam  made.  The  joints  are  all  "  milled," 
and  so  nicely  fitted  that  no  practicable  pressure  can  cause  leak- 


HISTORY  OF   THE   STEAM-BOILER-^ITS  STRUCTURE.     35 

age.     The  course  of  the  furnace  gases  and  the  water-circulation 
can  be  readily  traced  in  the  drawing. 

The  Root  Boiler  is  shown  in  Fig.  37,  differing  from  the  pre- 
ceding in  the  arrangement  of  tubes  and  their  connection.  The 
form  of  header  is  peculiar,  and  cannot  be  seen ;  but  the  general 
construction  is  well  shown  in  the  engraving.  In  various 
designs,  as  made  at  different  times  and  for  various  purposes, 
the  construction  has  been  somewhat  modified,  and  the  location, 


FIG.  37. — THE  ROOT  BOILER. 


size,  and  number  of  steam-drums  has  been  varied.  The  tubes 
are  four  or  five  inches  in  diameter,  and  usually  eight  or  ten  feet 
long. 

The  Harrison  Boiler  (Fig.  38)  consists  of  an  aggregation  of 
spheres,  of  cast-iron,  or  steel  as  now  made,  connected  by 
'"  necks"  of  somewhat  smaller  diameter.  These  spheres  are 
8  inches  in  diameter,  f  inch  thick,  capable  of  sustaining  a  pres- 
sure exceeding  100  atmospheres,  and  are  set  in  clusters,  as 
shown  in  the  sketch ;  they  are  fitted  together  with  faced  joints, 


30  THE   STEAM-BOILER. 

and  secured  by  long  bolts  passing  from  end  to  end  of  each  row. 
These  boilers  are  intended  to  be  so  proportioned  that  a  pres- 
sure far  less  than  that  which  would  produce  rupture  will 
stretch  the  bolts,  thus  allowing  each  joint  to  act  as  a  safety- 


FIG.  38. — THE  HARRISON  BOILER. 


valve.  The  three  types  of  boiler  which  have  just  been  de- 
scribed, and  their  various  modifications  are  the  most  common 
and  familiar  forms  of  sectional  boiler  in  use. 

The  Allen  Boiler  (Fig.  39)  has  only  been  constructed  ex- 
perimentally, and  has  never  come  into  the  general  market ;  but 
experiments  made  upon  it,  under  the  direction  of  a  committee 
of  the  American  Institute,  in  1871,  and  under  the  immediate 
direction  of  the  Author,  its  chairman,  gave  excellent  results, 
both  in  steaming  capacity  and  economy.  In  this  boiler  the 
tubes  are  suspended  by  one  end,  the  lower  end  being  closed,  as 
in  what  is  known  as  the  Field  system.  The  inclination  of  the 
tubes  30°  from  the  vertical  was  found  by  experiment  to  be  best. 
The  horizontal  cylinders  above,  to  one  of  which  each  line  of 
tubes  is  connected,  serve  as  circulating  tubes  and  passages  by 


HISTORY  OF   THE   STEAM-BOILER— ITS  STRUCTURE,      tf 

which  the  steam  made  is  conducted  to  the  steam-drum.  It 
will  be  noticed  that  the  whole  structure,  steam-drum  and  all,  is 
encased  in  the  brick-work  setting  and  exposed  to  contact  with 
the  heated  gases.  The  circulation  within  the  pendent  tubes 
was  excellent,  and,  with  pure  water  and  no  sediment  or  in- 


FIG.  39. — THE  ALLEN  BOILER. 


crustation  choking  them  at  their  lower  ends,  the  boiler  was 
considered  capable  of  doing  its  work  in  a  very  satisfactory 
manner. 

Fairbairn  has  remarked  that  "  danger  in  the  use  of  high- 
pressure  steam  does  not  consist  in  the  intensity  of  the  pressure 
to  which  the  steam  is  raised,  but  in  the  character  and  construc- 
tion of  the  vessel  which  contains  the  dangerous  element ;"  and 
this  remark  may  be  taken,  like  the  propositions  of  Col.  John 


THE   STEAM-BOILER. 


Stevens,  as  part  of  the  basis  of  the  philosophy  of  construction 
of  "  sectional "  boilers. 

22.  Marine  Sectional  Boilers  have  not  as  yet  come  into 
general  use,  although  many  attempts  have  been  made  to  in- 
troduce them.  The  first  boiler  built  by  John  Stevens  was 
intended  for  use  in  a  small  steam-vessel;  and  in  1825  or  1826 
Robert  L.  Thurston  and  John  Babcock,  then  of  Portsmouth, 
and  later  of  Providence,  R.  I.,  built  boilers  of  this  class,  con- 
sisting of  coils  of  pipe  within  which  the  water  and  steam  were 
contained,  the  fire  and  furnace  gases  passing  around  outside 
them.  Modifications  of  the  Root  boiler,  known  as  the  Belle- 
ville, and  others,  have  been  used  with  success  by  French  build- 
ers of  marine  machinery ;  and  the  Babcock  &  Wilcox  Co.  have 
produced  a  marine  boiler  like  that  shown  in  Fig.  40,  a  com- 
bination of  water-tubes  below  with  fire-tubes  and  steam-space 
above,  which  is  considered  a  good  form  for  use  at  sea. 

The  necessity  of  using  a  brick-work  setting  has  prevented 

the  introduction  of  the  common 
forms  at  sea.  Many  designs  are 
appearing  constantly,  and  it  is 
probably  only  a  question  of  time, 
when,  with  continually  rising 
steam-pressures,  the  older  forms 
will  be  displaced  by  these  modern 
and  safer  types. 

23.  The  Dates  of  Introduc- 
tion of  the  principal  devices  no- 
ticed in  modern  boilers  have  been 
given  by  Haswell,  who  describes 
the  various  familiar  forms  as  in- 
cluding the  dry-bridge  and  combustion-chamber  of  Wright 
(1756),  Darrance  (1845)  and  Baker  (1846);  the  dead-plate  of 
Watt  (1785);  the  water-bridge  of  Crampton  (1842)  and  Mills 
(1851);  the  air-bridge  of  Slater  (1831)  ;  the  horizontal  fire-tube 
of  Bolton  (1780),  of  Ericsson  (1828),  Seguin  and  Booth  (1829), 
and  of  Hawthorne  (1839)  an<^  Glasson  (1852);  the  vertical  fire- 
tube  of  Rumsey  (1788);  the  water-bottom  of  Allen  (1730)  and 
Fraser  (1827) ;  the  vertical  water-leg  of  Stephens  and  Hardley 


FIG.  40. — BABCOCK  &  WILCOX  MARINE 
BOILER. 


UlSTuKY   OF    THE    STEAM-BOILER— ITS  STRUCTURE,      39 

(1748),  Napier  (1842)  and  Dundonald  (1843);  the  steam-drum 
of  John  Stevens  (1803);  the  superheaters  of  Hately  (1768),  of 
English  (1809)  and  Allaire  (who  used  a  tall  steam-chimney  in 

1827). 

The  hanging  bridge  of  Johnson  (1818),  the  cylindrical 
return-flue  boiler  of  Napier  (1831),  the  cold-air  supply  above  the 
fire,  as  by  Thompson  (1796),  by  Robertson  (1800),  Arnott 
(1821),  and  by  Williams  (1839),  are  also>  he  states,  features  of 
the  modern  boiler.  The  introduction  of  the  water-tube  boiler 
by  Montgomery  has  not  led  to  a  change  of  type.* 

These  various  details  will  be  described  more  at  length  in 
later  chapters. 

24.  Peculiar  and  Special  Forms  of  Boiler  are  met  with 
in  all  departments.  Some  of  these  are  considerably  employed, 
and  in  many  cases  possess  special  features  of  advantage.  The 


FIG.  41. — THE  GALLOWAY  BOILER. 

Galloway  boiler  (Figs.  41,  42)  is  one  of  the  best  known  and  suc- 
cessful modifications  of  the  cylindrical  flue-boiler.  Its  special 
feature  is  the  conical  stay-tube,  which  is  used  to  increase  the 
heating-surface  and  to  strengthen  the  flue,  without  making  the 
heating-surface  difficult  of  access.  Large  numbers  of  these 
boilers  have  been  built  and  used  since  about  1860  in  Great 
Britain,  and  some  have  been  constructed  in  the  United 
States. 

*  Trans.  British  Institution  of  Naval  Architects,  1877. 


THE    STEAM-BOILER. 


The  exterior  is  a  plain  cylindrical  shell,  within  which  are 
two  cylindrical  furnaces  which  unite  in  one  flue,  having  parallel 


FIG.  42. — GALLOWAY  BOILER. 

curved  top  and  bottom,  struck  from  a  centre  below  the  boiler. 
In  this  flue  are  the  conical 
water-tubes,  each  10^  inches  di- 
ameter at  the  top  and  5^  inches 
diameter  at  the  bottom,  fixed  in 
a  radial  position  and  perpen- 
dicular to  the  top  and  bottom 
so  as  to  support  and  brace  the 
flue  and  to  intercept  and  break 
up  the  heated  gases  in  their  pas- 
sage from  the  furnaces.  Along 
the  sides  of  the  flue  there  are 


FIG.  43.— UPRIGHT  FLUE-BOILER. 


10  % 
FIG.  44.— FIRE-ENGINE  BOILER 


HISTORY   OF   THE   STEAM-BOILER— ITS  STRUCTURE.     41 

several  wrought-iron  pockets,  or  ''bafflers/'  which  deflect  the 
currents  and  cause  them  to  impinge  against  the  tubes  the 
end  pocket  providing  for  necessary  expansion  and  contraction. 
After  leaving  this  flue  the  gases  pass  along  the  sides  of  the 
shell  to  the  front  end,  thence  back  again  under  the  centre  of 
the  boiler  to  the  chimney. 

A  simple  form  of  upright  flue-boiler,  for  heating -purposes 
and  where  small  power  is  required,  is  seen  in  Fig.  43.  It  is 
of  simple  design,  and  easy  of  access  for  repair. 

A  steam  fire-engine  boiler  (Fig.  44),  as  built  by  the  Silsby 


BOTTOM  BLOW 


FIG.  45. — HERRESHOFF'S  BOILER. 

Co.  illustrates  the  use  of  the  Field  tubes,  pendent  from  the 
crown-sheet  of  the  furnace:  these  are  water-tubes,  but  the 
gases  pass  up  through  the  boiler  in  a  set  of  fire-tubes  seen  con- 
necting the  crown-sheet  with  the  top  of  the  boiler.  This  makes 
an  exceedingly  compact,  powerful,  and  light  steam-boiler. 


42  THE   STEAM-BOILER. 

The  Herreshoff  boiler  (Fig.  45),  as  constructed  for  fast 
yachts  and  torpedo-boats,  consists  of  a  cone-shaped  double 
coil  of  continuous  wrought-iron  pipe,  five  feet  to  five  and  a 
half  feet  in  diameter,  covered  by  a  disk  made  up  of  a  coil  of 
smaller  pipe.  The  feed-water  passes  through  the  latter,  and 
downward  through  the  boiler,  inside,  and  then  upward  again, 
through  the  outside  coil,  finally  passing  to  the  separator, 
whence  the  steam  passes  off  to  the  engine,  after  circulating 
through  the  three  top-coils  of  pipe  which  forms  a  super- 
heater, drying  and  superheating  the  steam  en  route.  The 
water  separated  from  the  steam  is  driven  back  into  the  boiler, 
with  the  feed-water,  by  the  feed  and  circulating  pumps.  The 
steam-pipe  used  in  making  up  the  boiler  is  lap-welded,  and 
from  if-  to  2f  inches  in  diameter  outside,  and  T3^  inch  in  thick- 
ness. This  boiler,  as  built  for  the  yacht  Leila,  contained  22 
cubic  feet  of  steam  and  water  space,  of  which  about  one  third 
was  steam-space ;  it  had  485  square  feet  of  heating-surface,. 
44  feet  of  superheating  area,  or  18.7  feet  of  heating-surface,, 
and  1.7  feet  of  superheating  surface,  per  square  foot  of  grate, 
these  areas  being  measured  on  the  exterior  of  the  tubes.  The 
boiler  developed  75  to  80  horse-power.  The  separator  is  ob- 
viously an  essential  feature  of  the  system. 

25.  Problems  in  Steam-boiler  Design  and  Construction 
are  among  the  most  interesting,  as  well  as  important,  which 
arise  in  the  practice  of  the  engineer.  These  problems  may, 
and  usually  do,  take  many  distinct  forms.  It  is  almost  invari- 
ably the  fact  that  the  quantity  of  steam  to  be  obtained  is 
specified  either  as  a  certain  weight  of  water  to  be  evaporated 
and  an  equal  weight  of  steam  to  be  furnished;  or  a  stated 
amount  of  power  is  to  be  given  through  a  specified  form  and 
cize  of  engine,  the  probable  efficiency  of  which  is  known  or  as- 
certainable;  or  a  stated  volume  of  building,  having  a  known 
exposure,  is  to  be  heated.  In  such  cases  the  problem  presented 
is  to  supply  the  steam  so  demanded  at  a  minimum  total  cost, 
using  a  type  of  boiler  to  be  selected  with  reference  to  the 
special  conditions  of  location  and  use. 

It  is  often  necessary,  when  dealing  with  a  large  "  plant,"  to 
determine  how  many  boilers  should  be  employed,  or  to  what 


HISTORY  OF    THE   STEAM-BOILER— ITS  STRUCTURE.     43 

extent  the  steam  made  should  be  divided  up  among  them: 
whether  a  larger  number  of  small  boilers  should  be  built  or 
fewer  large  boilers.  The  selection  of  the  best  type  for  a  speci- 
fied location  is  an  exceedingly  common  duty  of  the  engineer. 
To  secure  the  supply  of  a  given  quantity  of  steam  with  abso- 
lute safety,  or  with  reasonable  minimum  risk,  is  another  such 
problem.  The  usual  case  demands  the  production,  with  cer- 
tainty and  with  safety  to  life  and  property,  of  a  stated  weight 
of  steam,  day  by  day,  for  long  periods  of  time,  at  minimum 
average  total  expense  for  the  whole  period  of  life  of  the 
boilers. 

Problems  in  construction,  arising  in  connection  with  the 
design  and  application  of  steam-generators,  are  mainly  related 
to  the  best  methods  of  putting  together  the  parts  of  a  boiler 
of  which  the  design  has  been  made,  and  involve  the  continual 
application  of  a  good  knowledge  of  the  nature  and  uses  of  the 
materials  used,  and  especially  of  the  facts  and  principles  gov- 
erning the  strength  of  materials,  of  parts,  and  of  the  structure  as 
a  whole.  The  selection  of  the  best  form  of  joint  is  a  problem 
in  the  design  of  the  boiler;  but  the  determination  of  the  best 
method  of  making  that  joint  is  a  problem  in  construction. 
Such  are  all  questions  relating  to  the  actual  performance  of 
work  in  the  shop,  the  use  of  tools  in  the  work  of  building  the 
boiler,  and  the  comparison  of  methods. 

26.  Problems  in  the  Use  of  Steam-boilers  are  not  less 
important   and  difficult  of  solution,  often,   than   those  which 
arise  in  the  production  of  the  design   or  in  its  construction. 
How  to  obtain  a  maximum  quantity  of  steam  ;  how  to  secure 
dryness  and  uniformity  of  quality ;  how  to  prolong  the  life  of 
the  structure ;  and  how  to   effect  its  preservation   most  effec- 
tively, at  least  cost  in  time,  money,  or  loss  of  use — are  only  a 
few  examples  of  the  many  problems  that  continually  present 
themselves  for  immediate  solution  while  the  boiler  is  in  ser- 
vice. 

27.  The  General  Method  of  Solution   of  Problems   in 
Design  is  to  study  the  case  very  carefully  in  the  light  of  all 
information  that  can  be  gained  relating  to  the  special  conditions 
affecting  it,  and  then,  by  comparison  of  the  results  of  experi- 


44  THE   STEAM-BOILER. 

ence  with  various  boilers  under  as  nearly  as  may  be  similar 
conditions,  determining  the  best  form  for  the  case  in  hand. 
The  designing  engineer  next  endeavors  to  effect  such  improve- 
ment as  his  own  talent  and  experience  may  enable  him  to 
originate,  with  a  view  to  the  most  perfect  possible  adaptation 
of  the  design  to  its  purposes.  He  next  settles  the  general  pro- 
portions, the  forms  of  details,  and  finally  the  absolute  dimen- 
sions and  exact  proportions.  So  much  being  done,  he  is  pre- 
pared to  make  a  preliminary  study,  which  deliberately  made 
alterations  may  convert  into  a  finally  complete  design. 


CHAPTER   II. 

MATERIALS — STRENGTH    OF    MATERIALS    AND   OF    THE   STRUC- 
TURE. 

28.  The  Quality  of  the  Material  used  in  the  construc- 
tion of  steam-boilers  must  obviously  be  very  carefully  consid- 
ered. Not  only  is  the  steam-boiler  expected  to  bear  great 
strains  and  high  pressures,  but  the  terrible  consequences  which 
are  liable  to  follow  its  rupture  make  it  important  that  it  should 
sustain  its  load  and  do  its  work  with  the  most  absolute  safety 
attainable.  The  structure  is  exposed  to  greater  variety  of  con- 
ditions tending  to  weaken  it  and  to  shorten  its  life  than  any 
other  apparatus  familiar  to  the  engineer ;  and  the  results  of  its 
failure  are  more  certain  to  be  disastrous  to  human  life,  as  well 
as  to  property.  All  parts  of  the  boiler  are,  while  under  heavy 
stress,  exposed  to  continually  changing  temperatures,  with, 
usually,  occasional  variations  extending  over  two  hundred  or 
more  degrees  Fahrenheit.  Nearly  every  part  is  liable  to  cor- 
rosion, often  of  a  kind  which  is  the  more  dangerous  because 
very  difficult  to  detect  or  to  gauge.  The  boiler  is  very  liable 
to  be  subjected  to  peculiarly  severe  stresses  due  to  accidental 
circumstances  and  to  excessive  steam-pressure  or  to  deficiency 
of  water. 

The  material  needed  for  the  purposes  of  the  boiler-maker 
should  for  all  these  reasons  b'e  as  strong,  tough,  and  ductile 
as  it  can  possibly  be  made.  Of  these  qualities  it  is  evident 
that  ductility,  capability  of  bearing  violent  alteration  of  form 
without  fracture,  is  even  more  vitally  essential  than  strength. 
A  lack  of  tenacity  can  be  met  by  using  more  metal,  but  noth- 
ing can  make  amends  for  brittleness.  Good  boiler-plate  must 
possess  great  strength,  and  must  combine  with  it  great  ductil- 
ity—must have  high  elastic  and  total  "  resilience,"  as  such  a 
combination  is  termed. 


46  THE   STEAM-BOILER. 

The  various  parts  of  the  boiler  require  their  material  to 
exhibit  somewhat  different  special  qualities :  tubes  must  be 
tough  enough  to  bear  the  "  upsetting"  action  of  the  "  ex- 
pander" by  which  they  are  secured  in  the  tube-sheets,  and  yet 
must  be  hard  enough  to  sustain  reasonably  well  the  abrading 
effect  of  cinder-laden  currents  of  gas ;  flue-sheets  and  especially 
furnace-sheets  must  be  hard,  and  capable  of  resisting  both  the 
mechanical  wear  and  the  corrosive  action  of  the  furnace-gases 
and  their  burden  of  coal,  ash,  and  cinder,  and  must  at  the  same 
time  sustain  safely  the  continual  variation  of  temperature  to 
which  they  are  subjected  by  the  alternate  impact  of  flame  and 
of  cold  air  as  the  fires  are  worked.  The  "  shell  "  of  the  tjoiler 
is  less  affected  by  such  stresses ;  but  it  nevertheless  must  meet 
with  a  greater  variety  of  loading,  in  a  greater  number  of  direc- 
tions, than  perhaps  any  other  known  iron  structure ;  every 
change  of  pressure  within  it,  every  alteration  of  temperature, 
every  rise  or  fall  of  the  water-line,  produces  a  variation  of  the 
amount  and  direction  of  the  stresses  to  which  its  metal  and 
joints  are  exposed.  Great  tenacity  combined  with  ductility  is 
the  essential  characteristic  of  all  material  used  in  the  construc- 
tion of  steam-boilers. 

29.  The  Principles  Relating  to  the  Strength  of  Mate- 
rials of  construction,*  and  other  qualities  useful  in  resisting 
the  strains  to  which  steam-boilers  are  subject,  are  very  simple 
and,  in  the  main,  well  established. 

The  Resistance  of  Metal  to  rupture  may  be  brought  into 
play  by  either  of  several  methods  of  stress,  which  have  been 
thus  divided  by  the  Author: 

j  Tensile  :  resisting  pulling  force. 
ina      '     '     '      (  Compression  :  resisting  crushing  force. 

r  Shearing  :  resisting  cutting  across. 

Transverse        .     .     .      J  Bending :  resisting  cross  breaking. 
(  Torsional :  resisting  twisting  stress. 

When  a  load  is  applied  to  any  part  of  a  structure  or  of  a 
machine  it  causes  a  change  of  form,  which  may  be  very  slight, 

*  Abridged  and  adapted  from  Part  II.,  Chapter  IX.,  "  Materials  of  Engineer- 
ing, "  by  the  Author. 


MATERIALS— STRENGTH  OF   THE   STRUCTURE.  4/ 

"but  which  always  takes  place,  however  small  the  load.  This 
change  of  form  is  resisted  by  the  internal  molecular  forces  of 
the  piece,  i.e.,  by  its  cohesion.  The  change  of  form  thus  pro- 
duced is  called  strain,  and  the  acting  force  is  a  stress. 

The  Ultimate  Strength  of  a  piece  is  the  maximum  resist- 
ance under  load — the  greatest  stress  that  can  exist  before  rup- 
ture. The  Proof  Strength  is  the  load  applied  to  determine  the 
value  of  the  material  tested  when  it  is  not  intended  that  ob- 
servable deformation  shall  take  place.  It  is  usually  equal,  or 
nearly  so,  to  the  maximum  elastic  resistance  of  the  piece.  It 
is  sometimes  said  that  this  load,  long  continued,  will  produce 
fracture ;  but,  as  will  be  seen  hereafter,  this  is  not  necessarily, 
•even  if  ever,  true. 

The  Working  Load  is  that  which  the  piece  is  proportioned 
to  bear.  It  is  the  load  carried  in  ordinary  working,  and  is 
usually  less  than  the  proof  load,  and  is  always  some  fraction, 
determined  by  circumstances,  of  the  ultimate  strength. 

A  Dead  Load  is  applied  without  shock,  and  once  applied 
remains  unchanged,  as,  e.g.,  the  weight  of  a  bridge  ;  it  produces 
a  uniform  stress.  A  Live  Load  is  applied  suddenly,  and  may 
produce  a  variable  stress,  as,  e.g.,  by  the  passage  of  a  railway 
train  over  a  bridge. 

The  Distortion  of  the  strained  piece  is*  related  to  the  load 
In  a  manner  best  indicated  by  strain-diagrams.  Its  value  as 
a  factor  of  the  measure  of  shock-resisting  power,  or  of  resilience, 
is  exhibited  in  a  later  article.  It  also  has  importance  as  indi- 
cating the  ductile  qualities  of  the  metal. 

The  Reduction  of  Area  of  Section  under  a  breaking  load  is 
•similarly  indicative  of  the  ductility  of  the  material,  and  is  to 
be  noted  in  conjunction  with  the  distortion. 

E.g.,  a  considerable  reduction  of  section  with  a  smaller  pro- 
portional extension  would  indicate  a  lack  of  homogeneousness, 
and  that  the  piece  had  broken  at  the  soft  part  of  the  bar. 
The  greater  the  extension  in  proportion  to  the  reduction 
of  area  in  tension,  the  more  uniform  the  character  of  the 
metal. 

Factors  of  Safety. — The  ultimate  strength,  or  maximum 
capacity  for  resisting  stress,  has  a  ratio  to  the  maximum  stress 


48 


THE   STEAM-BOILER. 


due  to  the  working  load,  which,  although  less  in  metal  than  in 
wooden  or  stone  structures,  is  nevertheless  made  of  consider- 
able magnitude  in  many  cases.  It  is  much  greater  under  mov- 
ing than  under  steady  "  dead  "  loads,  and  varies  with  the  char- 
acter of  the  material  used.  For  machinery  it  is  usually  6  or  8 ; 
for  structures  erected  by  the  civil  engineer,  from  4  to  6.  The 
following  may  be  taken  as  minimum  values  of  this  "  factor  of 
safety"  for  the  metals  : 


MATERIAL. 

LOAD. 

SHOCK. 

Dead. 

Live. 

Iron  and   steel,  copper  and 
other  soft  metals 

5 
4 

8 
7 

10  + 

10  to  15 

Ratio  of  ultimate 
strength  to 
working  load. 

The  brittle  metals  and  alloys 

The  Proof  Strength  usually  exceeds  the  working  load  from 
50  per  cent  with  tough  metals,  to  200  or  300  per  cent  where 
brittle  materials  are  used.  It  should  usually  be  below  the  elas- 
tic limit  of  the  material. 

As  this  limit,  with  brittle  materials,  is  often  nearly  equal  to 
their  ultimate  strength,  a  set  of  factors  of  safety,  based  on  the 
elastic  limit,  would  differ  much  from  those  above  given  for 
ductile  metals,  but  would  be  about  the  same  for  all  brittle  ma- 
terials, thus: 


LOAD. 

Dead. 

Live. 

Ratio  of  elastic 

Ferrous  and  soft  metals.  .  .  . 

2 

4 

6 

Resistance  to 

Brittle  metals  and  alloys.  .  . 

3 

6 

8  to  12 

working  load. 

The  figure  given  for  shock  is  to  be  taken  as  approximate, 
but  used  only  when  it  is  not  practicable  to  calculate  the  energy 
of  impact  and  the  resilience  of  the  piece  meeting  it,  and  thus 
to  make  an  exact  calculation  of  proportions. 

The  Measure  of  Resistance  to  Strain  is  determined  in  form 


MATERIALS—  STRENGTH  OF    THE   STRUCTURE.  49 

by  the  character  of  the  stress.  By  stress  is  here  understood 
the  force  exerted,  and  by  strain  the  change  of  form  produced 
by  it. 

Tenacity  is  resistance  to  a  pulling  stress,  and  is  measured 
by  the  resistance  of  a  section,  one  unit  in  area,  as  in  pounds 
or  tons  on  the  square  inch,  or  in  kilogrammes  per  square  cen- 
timetre or  square  millimetre.  Then  if  T  represents  the  te- 
nacity and  K  is  the  section  resisting  rupture,  the  total  load 
that  can  be  sustained  is,  as  a  maximum, 


(i) 


Compression  is  similarly  measured,  and  if  C  be  the  maxi- 
mum resistance  to  crushing  per  unit  of  area,  and  K  the  section, 
the  maximum  load  will  be 

P=CK.     ........    (2) 

Shearing  is  resisted  by  forces  expressed  in  the  same  way, 
and  the  maximum  shearing  stress  borne  by  any  section  is 

P=SK.     .......    (3) 

Bending  Stresses  are  measured  by  moments  expressed  by 
the  product  of  the  bending  effort  into  its  lever-arm  about  the 
section  strained,  and  if  P  is  the  resultant  load,  /  the  lever-arm,. 
and  M  the  moment  of  resistance  of  the  section  considered, 

Pl=M.      ........    (4) 

Torsional  Stresses  are  also  measured  by  the  moment  of  the 
stress  exerted,  and  the  quantity  of  attacking  and  resisting  mo- 
ments is  expressed  as  in  the  last  case. 

Elasticity  is  measured  by  the  longitudinal  force,  which,  act- 
ing on  a  unit  of  area  of  the  resisting  section,  if  elasticity  were 
to  remain  unimpaired,  would  extend  the  piece  to  double  its 
original  length.  Within  the  limit  at  which  elasticity  is  unim- 
paired, the  variation  of  length  is  proportional  to  the  force  act- 
ing, and  if  E  is  the  "Modulus  of  Elasticity"  or  "Young's  Mod- 


5<D  THE   STEAM-BOILER. 

ulus,"  /  the  length,  and  e  the  extension,  P  being  the  total  load, 
and  K  the  section, 

£  =  -;.    .......    (5) 


The  Coefficients  entering  into  these  several  expressions  for 
resistance  of  materials  are  often  called  Moduli,  and  the  forms 
of  the  expressions  in  which  they  appear  are  deduced  by  the 
Theory  of  the  Resistance  of  Materials,  and  the  processes  are 
given  in  detail  in  works  on  that  subject. 

These  moduli  or  coefficients,  as  will  be  seen,  have  values 
which  are  rarely  the  same  in  any  two  cases ;  but  vary  not  only 
with  the  kind  of  material,  but  with  every  variation,  in  the  same 
substance,  of  structure,  size,  form,  age,  chemical  composition 
or  physical  character,  with  every  change  of  temperature,  and 
even  with  the  rate  of  distortion  and  method  of  action  of  the 
distorting  force.  Values  for  each  familiar  material,  for  a  wide 
range  of  conditions,  will  be  given  in  the  following  pages. 

When  a  piece  of  metal  is  subjected  to  stress  exceeding  its 
power  of  resistance  for  the  moment,  and  gradually  increasing 
up  to  the  limit  at  which  rupture  takes  place,  it  yields  and  be- 
comes distorted  at  a  rate  which  has  a  definitely  variable  rela- 
tion to  the  magnitude  of  the  distorting  force ;  this  relation,  al_ 
though  very  similar  for  all  metals  of  any  one  kind,  differs 
greatly  for  different  metals,  and  is  subject  to  observable  altera- 
tion by  every  measurable  difference  in  chemical  composition  or 
in  physical  structure. 

Thus  in  Fig.  46  let  this  operation  be  represented  by  the 
several  curves  a,  b,  c,  d,  etc.,  the  elevation  of  any  point  on  the 
curve  above  the  axis  of  abscissas,  OX,  being  made  proportional 
to  the  resistance  to  distortion  of  the  piece,  and  to  the  equiva- 
lent distorting  stress,  at  the  instant  when  its  distance  from  the 
left  side  of  the  diagram,  or  the  axis  of  ordinates,  O  Y,  measures 
the  coincident  distortion.  As  drawn,  the  strain-diagram,  a  a\ 
is  such  as  would  be  made  by  a  soft  metal  like  tin  or  lead  ;  b  b' 


MATERIALS— STRENGTH  OF   THE    STRUCTURE.  5  I 

represents  a  harder,  and  c  c'  a  still  harder  and  stronger  metal, 
as  zinc  and  rolled  copper.  If  the  smallest  divisions  measure 
the  per  cent  of  extension  horizontally,  and  10,000  pounds  per 
square  inch  (703  kilogrammes  per  square  centimetre)  vertically, 
d  d'  would  fairly  represent  a  hard  iron,  or  a  puddled  or  a 
"  mild  "  steel;  while//7  and  •  g  g'  would  be  strain-diagrams  of 
hard  and  of  very  hard  tool  steels,  respectively. 

The  points  marked  e,  e',  e" ,  etc.,  are  the  so-called  "  elastic 
limits"  at  which  the  rate  of  distortions  more  or  less  suddenly 
changes,  and  the  elevation  becomes  more  nearly  equal  to  the 
permanent  change  of  form,  and  at  these  points  the  resistance 
to  further  change  increases  much  more  slowly  than  before. 


<i_. 


/h 


m 


FIG.  46. — STRAIN-DIAGRAMS. 

This  change  of  rate  in  increase  in  resistance  continues  until  a 
maximum  is  reached,  and,  passing  that  point,  the  piece  either 
breaks,  as  at  /;  and  g' ,  or  yields  more  and  more  easily  until  dis- 
tortion ceases,  or  until  fracture  takes  place,  and  it  becomes  zero 
at  the  base-line,  as  at  X. 

Such  curves  have  been  called  by  the  Author  "  Strain-dia- 
grams." 

If  at  any  moment  the  stress  producing  distortion  is  relaxed, 
the  piece  recoils  and  continues  this  reversed  distortion  until, 
all  load  being  taken  off,  the  recoil  ceases  and  the  piece  takes 
its  "  permanent  set."  This  change  is  shown  in  the  figure  at 
f"  f",  the  gradual  reduction  of  load  and  coincident  partial  res- 
toration of  shape  being  represented  by  a  succession  of  points 


52  THE   STEAM-BOILER. 

forming  the  line  /"/",  each  of  which  points  has  a  position 
which  is  determined  by  the  elastic  resistance  of  the  piece  as 
now  altered  by  the  strain  to  which  it  has  been  subjected.  The 
distance  Of"  measures  the  permanent  set,  and  the  distance 
f"  f"  measures  the  recoil. 

The  piece  now  has  qualities  which  are  quite  different  from 
those  which  distinguished  it  originally,  and  it  may  be  regarded 
as  a  new  specimen  and  as  quite  a  different  metal.  Its  strain- 
diagram  now  has  its  origin  at  f",  and  the  piece  being  once 
more  strained,  its  behavior  will  be  represented  by  the  curve 
f  f"  evl  f',  a  curve  which  often  bears  little  resemblance  to  the 
original  diagram  6>, //'.  The  new  diagram  shows  an  elastic 
limit  at  ev\  and  very  much  higher  than  the  original  limit  elv. 
Had  this  experiment  been  performed  at  any  other  point  along 
the  line//',  the  same  result  would  have  followed.  It  thus  be- 
comes evident  that  the  strain-diagram  is  a  curve  of  elastic 
limits,  each  point  being  at  once  representative  of  the  resistance 
of  the  piece  in  a  certain  condition  of  distortion,  and  of  its 
elastic  limit  as  then  strained. 

The  ductile,  non-ferrous  metals,  and  iron  and  steel  and  the 
truly  elastic  substances,  have  this  in  common — that  the  effect 
of  strain  is  to  produce  a  change  in  the  mode  of  resistance  to 
stress,  which  results  in  the  latter  in  the  production  of  a  new 
and  elevated  elastic  limit,  and  in  the  former  in  the  introduction 
of  such  a  limit  where  none  was  observable  before. 

It  becomes  necessary  to  distinguish  these  elastic  limits  in 
describing  the  behavior  of  strained  metals,  and,  as  will  be  seen 
subsequently,  the  elastic  limits  here  described  are  under  some 
conditions  altered  by  strain,  and  we  thus  have  another  form  of 
elastic  limit  to  be  defined  by  a  special  term. 

In  this  work  the  original  elastic  limit  of  the  piece  in  its  or- 
dinary state,  as  at  e,  e',  e" ,  etc.,  will  be  called  either  the  Origi- 
nal or  the  Primitive,  Elastic  Limit,  and  the  elastic  limit  cor- 
responding to  any  point  in  the  strain-diagram  produced  by 
gradual,  unintermitted  strain  will  be  called  the  Normal  Elastic 
Limit  for  the  given  strain.  It  is  seen  that  the  diagram  repre- 
senting this  kind  of  strain  is  a  Curve  of  Normal  Elastic  Limits. 

The  elastic  limit  is  often  said  to  be  that  point  at  which  a 


MATERIALS— STRENGTH  OF   THE   STRUCTURE.  53 

permanent  set  takes  place.  As  will  be  seen  on  studying  actual 
strain-diagrams  to  be  hereafter  given,  and  which  exhibit  accu- 
rately the  behavior  of  the  metal  under  stress,  there  is  no  such 
point.  The  elastic  limit  referred  to  ordinarily,  when  the  term 
is  used,  is  that  point  within  which  recoil  on  removal  of  load  is 
approximately  equal  to  the  elongation  attained,  and  beyond 
which  set  becomes  nearly  equal  to  total  elongation. 

It  is  seen  that,  within  the  elastic  limit,  sets  and  elongations 
are  similarly  proportional  to  the  loads,  that  the  same  is  true 
on  any  elastic  line,  and  that  loads  and  elongations  are  nearly 
proportional  everywhere  beyond  the  elastic  limit,  within  a 
moderate  range,  although  the  total  distortion  then  bears  a  far 
higher  ratio  to  the  load,  while  the  sets  become  nearly  equal  to 
the  total  elongations. 

The  behavior  of  metals  under  moving  or  "live"  load  and 
under  shock  is  not  the  same  as  when  gradually  and  steadily 
strained  by  a  slowly  applied  or  static  stress.  In  the  latter  case 
the  metal  undergoes  the  changes  illustrated  by  the  strain- 
diagrams,  until  a  point  is  reached  at  which  equilibrium  occurs 
between  the  applied  load  and  resisting  forces,  and  the  body 
rests  indefinitely,  as  under  a  permanent  load,  without  other 
change  occurring  than  such  settlement  of  parts  as  will  bring 
the  whole  structural  resistance  into  play. 

When  a  freely  moving  body  strikes  upon  the  resisting 
piece,  on  the  other  hand,  it  only  comes  to  rest  when  all  its 
kinetic  energy  is  taken  up  by  the  resisting  piece ;  there  is  then 
an  equality  of  vis  viva  expended  and  work  done,  which  is  ex- 
pressed thus: 

WV* 

(7) 


in  which  expression  W  is  the  weight  of  the  striking  body,  V 
its  velocity,  /  the  resisting  force  at  any  instant,  pm  the  mean 
resistance  up  to  the  point  at  which  equilibrium  occurs,  and  s  is 
the  distance  through  which  resistance  is  met. 

As  has  been  seen,  the  resistance  may  usually  be  taken  as 
varying  approximately  with  the  ordinates  of  a  parabola,  the 


54  THE   STEAM-BOILER. 

abscissas  representing   extensions.      The  mean    resistance    is, 
therefore,  nearly  two  thirds  the  maximum,  and 


/>* 

-  —    I  pdx  =  pms  =  \et  =  «*Y  nearly,   .     .     (8) 

£"  t/o 


where  e  is  the  extension,  and  t  the  maximum  resistance  at 
that  extension,  and  a  a  constant.  Brittle  materials,  like  hard 
bronzes  and  brasses,  have  a  straight  line  for  their  strain-dia- 
grams, and  the  coefficient  becomes  -J  instead  of  f  ,  and 


Resilience,  or  Spring,  is  the  work  of  resistance  up  to  the 
elastic  limit.  This  will  be  called  Elastic  Resilience.  The  mod- 
ulus of  elasticity  being  known,  the  Modulus  of  Elastic  Resili- 
ence is  obtained  by  dividing  half  the  square  of  the  maximum 
elastic  resistance  by  the  modulus  of  elasticity,  E,  as  above,  and 
the  work  done  to  the  "  primitive  elastic  limit"  is  obtained  by 
multiplying  this  modulus  of  resilience  by  the  volume  of  the 
bar.* 

The  total  area  of  the  diagram,  measuring  the  total  work 
done  up  to  rupture,  will  be  called  a  measure  of  Total  or  Ulti- 
mate Resilience.  Mallett's  Coefficient  of  Total  Resilience  is 
the  half  product  of  maximum  resistance  into  total  extension. 
It  is  correct  for  brittle  substances  and  all  cases  in  which  the 
primitive  elastic  limit  is  found  at  the  point  of  rupture.  With 
tough  materials,  the  coefficient  is  more  nearly  two  thirds  — 
and  may  be  even  greater  where  the  metal  is  very  ductile,  asr 
e.g.,  pure  copper,  tin,  or  lead.  Unity  of  length  and  of  section 
being  taken,  this  coefficient  is  here  called  the  Modulus  of 
Resilience. 

When  the  energy  of  a  striking  body  exceeds  the  total  re- 
silience of  the  material,  the  piece  will  be  broken.  When  the 


Rankine  and  some  other  writers  take  this  modulus  as  —  instead  of  -—  . 

E  2,E 


MATERIALS— STRENGTH  OF   THE    STRUCTURE.  55 

energy  expended  is  less,  the  piece  will  be  strained  until  the 
work  done  in  resistance  equals  that  energy,  when  the  striking 
body  will  be  brought  to  rest. 

As  the  resistance  is  partly  due  to  the  inertia  of  the 
particles  of  the  piece  attacked,  the  strain-diagram  area  is 
always  less  than  the  real  work  of  resistance,  and  at  high  ve- 
locities may  be  very  considerably  less,  the  difference  being 
expended  in  the  local  deformation  of  that  part  of  the  piece 
at  which  the  blow  is  received.  In  predicting  the  effect  of  a 
shock  it  is,  therefore,  necessary  to  know  not  only  the  energy 
stored  in  the  moving  mass  and  the  method  of  variation  of  the 
resistance,  but  also  the  striking  velocity.  To  meet  a  shock 
successfully,  it  is  seen  that  resilience  must  be  secured  sufficient 
to  take  up  the  shock  without  rupture,  or,  if  possible,  without 
serious  deformation.  It  is  in  most  cases  necessary  to  make 
the  elastic  resilience  greater  than  the  maximum  energy  of  any 
attacking  body. 

Moving  Loads  produce  an  effect  intermediate  between  that 
due  to  static  stress  and  that  due  to  the  shock  of  a  freely  mov- 
ing body  acting  by  its  inertia  wholly ;  these  cases  are,  there- 
fore, met  in  design  by  the  use  of  a  high  factor  of  safety,  as 
above. 

As  is  seen  by  a  glance  at  the  strain-diagram,  ff  (Fig.  46),  the 
piece  once  strained  has  a  higher  elastic  resilience  than  at  first, 
and  it  is  therefore  safer  against  permanent  distortion  by  mod- 
erate shocks,  while  the  approach  of  permanent  extension  to  a 
limit  renders  it  less  secure  against  shocks  of  such  great  inten- 
sity as  to  endanger  the  piece. 

When  the  shock  is  completely  taken  up,  the  piece  recoils, 
as  at  e^f'f",  until  it  settles  at  such  a  point  on  that  line — as- 
suming the  shock  to  have  extended  the  piece  to  the  point  evi 
—that  the  static  resistance  just  equilibrates  the  static  load. 
This  point  is  usually  reached  after  a  series  of  vibrations  on 
either  side  of  it  has  occurred.  With  perfect  elasticity,  this 
point  is  at  one  half  the  maximum  resistance,  or  elongation, 
attained.  Thus  we  have 


56  THE   STEAM-BOILER. 

but/  varies  as  A  x  within  the  elastic  limit,  which  limit  has  now 
risen  to  some  new  point  along  the  line  of  normal  elastic  limits, 
as  e*.  Taking  the  origin  at  the  foot  of  /"/"»  since  tne  varia- 
tions of  length  along  the  line  Ox  are  equal  to  the  elongations 
and  to  the  distances  traversed  as  the  load  falls,  and  as  stresses 
are  now  proportional  to  elongations, 

p  —  ax\     W/t=Ws',     and     W=P\.     .     .     (11) 

when  the  resisting  force  is  /,  the  elongations  x,  while  h  and  s 
are  maximum  fall  and  elongation,  and  P  is  the  maximum 
resistance  to  the  load  at  rest.  Then 

r*  fs  a  2  2^          f     x 

/  pdx  —  a  I  xdx  =  -s?  =  Ws;     :.  s  =  -  .    .     (12) 
J0  *  Jo  2  a 

For  a  static  load,  if  s'  is  the  elongation, 

W 
W  =  P  =  as'-,     .'.  s'  =  —. 

Hence, 

• 


and  the  extension  and  the  corresponding  stress  due  to  the 
sudden  application  of  a  load  are  double  those  produced  by  a 
static  load. 

Where  the  applied  load  is  a  pressure  and  not  a  weight, 
i.e.,  where  considerable  energy  in  a  moving  body  is  not  to  be 
absorbed,  as  in  the  action  of  steam  in  a  steam-engine,  the 
only  increase  of  strain  produced  by  a  suddenly  applied  load  is 
that  produced  by  the  inertia  of  such  of  those  parts  of  the  mass 
attacked  as  may  have  taken  up  motion  and  energy. 

30.  Tenacity,  Elasticity,  Ductility,  and  Resilience  are 
the  four  essential  qualities  of  a  good  material  for  use  in  steam- 
boiler  construction.  In  some  cases,  the  relative  values  of 


MATERIALS— STRENGTH   OF    THE   STRUCTURE.  $? 

these  several  properties  are  very  different  from  that  relation  in 
others.  For  example :  while  boiler-iron  or  steel  must  have 
ductility,  even  if  tenacity  is  sacrificed  to  some  extent  to  secure 
it,  machinery  irons  and  steels  should  have  a  certain  amount  of 
rigidity,  and  tool-steel  a  minimum  allowable  hardness,  as  their 
leading  characteristics ;  and  in  all,  the  essential  property  being 
securjed,  as  good  a  combination  of  all  the  other  valuable  prop- 
erties is  sought  as  can  possibly  be  obtained. 

The  problem  of  proportioning  parts  to  resist  shock  is  seen 
to  involve  a  determination  of  the  energy,  or  "  living  force,"  of 
the  load  at  impact,  and  an  adjustment  of  proportion  of  sec- 
tion and  shape  of  piece  attacked  such  that  its  work  of  elastic 
or  of  ultimate  resilience,  whichever  is  taken  as  the  limit,  shall 
exceed  that  energy  in  a  proportion  measured  by  the  factor  of 
safety  adopted.  For  ordinary  live  loads  and  moderate  impact, 
requiring  no  specially  detailed  consideration,  the  factors  of 
safety  already  given,  as  based  upon  ultimate  strength  simply, 
are  considered  sufficient ;  in  all  cases  of  doubt,  or  when  heavy 
shock  is  anticipated,  calculations  of  energy  and  resilience  are 
necessary,  and  these  demand  a  complete  knowledge  of  the 
character,  chemical,  physical,  and  structural,  of  every  piece 
involved,  of  its  resilience  and  method  of  yielding  under  stress, 
and  of  every  condition  influencing  the  application  of  the  at- 
tacking force — in  other  words,  a  complete  knowledge  of  the 
material  used,  of  the  members  constructed  of  it,  and  of  the 
circumstances  likely  to  bring  about  its  failure. 

The  form  of  such  parts  should  usually  be  determined  on 
the  assumption  that  deformation  may  some  time  occur;  and 
such  expedients  as  that  of  Hodgkinson  in  enlarging  the  sec- 
tion on  the  weaker  side,  as  well  as  the  adoption  of  a  larger 
factor  of  safety  based  on  ultimate  strength,  are  advisable. 

31.  The  Chemical  and  Physical  Characteristics  of  Iron 
determines  the  value  of  the  metal  for  the  purpose  of  the  engi- 
neer in  construction.  The  following  .set  of  strain-diagrams 
(Fig.  47)  may  be  taken  as  representative  of  the  behavior  of 
good  samples  of  the  various  grades  of  wrought-iron  and  of 
steel  above  described. 

The  diagrams  a  a,  b  b,  c  c,  are  those  of  commercial  irons  of 


THE    STEAM-BOILER. 


good  quality,  soft,  medium,  and  hard  respectively,  and  all  of 
high  ductility.  The  elastic  limits  of  a  and  b  differ  greatly  in 
position,  and  the  irons  themselves  are  characteristically  differ- 
ent. The  one  is  in  a  condition  of  initial  internal  strain  which 
has  weakened  it  against  external  stresses ;  but  that  strain  being 
relieved  by  flow  under  strain,  the  iron  is  finally  found  to  be 
stronger  than  the  second  piece. 

It  is  evident  that  the  first  is  less  valuable  than  the  second, 


Lbs.~peiSq.lnch. 
120.000 


Kil's;perS.q.Cnn. 
843ft 


Elongation  per  Cent 


FIG 


-DIAGRAMS    OF    IRON   AND    STEEL. 


however,  under  any  stresses  that  occur  within  the  usual  limits 
of  distortion  ;  the  engineer  would  choose  b  as  having  a  higher 
elastic  limit  and  much  greater  elastic  resilience. 

The  "  elasticity  line,"  e'  /,  shows  the  amount  of  spring  and 
of  set  at  the  point  at  which  it  is  taken,  and  gives  a  measure  of 
the  modulus  of  elasticity.  The  harder  iron,  d  d,  is  probably 
actually  a  puddled  steel,  and  has  been  made  by  balling  up  the 
sponge  in  the  puddling  furnace  too  early  to  permit  complete 


MATERIALS— STRENGTH  OF   THE   STRUCTURE.  59 

reduction  of  carbon.  The  gradual  increase  in  strength,  with  in- 
crease of  carbon,  and  rise  of  the  elastic  limit,  are  shown,  as  well 
as  the  coincident  loss  of  ductility,  in  the  diagrams,  e,  ft  g,  and 
//,  which  are  those  of  steels  containing  from  0.35  to  I  per  cent 
carbon  ;  e  and /are  the  diagrams  from  excellent  samples  of  the 
product  of  the  open-hearth  and  pneumatic  processes,  and  the 
stronger  specimens  are  representatives  of  the  average  crucible 
steel. 

The  increase  of  resilience  within  the  elastic  range  is  seen  to 
be  very  great  as  the  percentage  of  carbon  is  increased. 

The  chemical  composition  of  iron  and  steel  determines  the 
real  character  of  any  sample,  although  differences  of  physical 
character  and  of  molecular  structure  often  seriously  modify  the 
value  of  pieces  into  the  composition  of  which  they  enter. 
With  cast  metal,  where  sound  castings  have  been  secured,  the 
chemical  constitution  of  the  metal  being  known  from  analyses, 
the  value  of  the  metal  for  purposes  of  construction  may  be 
usually  well  judged  ;  and  a  comparison  of  the  data  given  by 
the  chemist  with  the  specific  gravity  of  the  metal,  will  gener- 
ally be  sufficient  to  determine  its  character  with  great  exact- 
ness. Specifications  for  cast-iron  or  cast-steel  may  usually  be 
safely  so  drawn  as  to  make  the  acceptance  of  the  material  de- 
pendent upon  accordance  with  specified  formulas  of  composi- 
tion and  density. 

Thus :  A  good,  gray  foundry  iron,  free  from  phosphorus 
and  low  in  silicon,  and  having  a  density  of  7.25  to  7.28,  is,  un- 
less containing  some  peculiar  and  unusual  constituent  in  excess, 
a  safe  iron  to  use  for  all  purposes  demanding  strength  Wrought- 
iron  and  "  mild  "  steels  are,  on  the  other  hand,  so  greatly  mod- 
ified by  the  processes  of  preparation  in  the  mill,  that  actual 
test  can  only  be  safely  depended  upon  to  determine  their  value 
in  construction. 

Statements  of  the  strength  of  iron  or  steel  are  not  of  great 
value  in  any  case,  when  the  metal  of  which  the  strength  or 
ductility  is  given  is  specified  by  its  trade  or  generic  name  sim- 
ply without  a  statement  of  its  precise  chemical  composition  and 
physical  character.  Wrought-iron  varies  in  composition  and  in 
structure  to  such  an  extent  that,  while  the  softest  and  purest 


60  THE   STEAM-BOILER. 

varieties  often  have  a  tenacity  of  but  about  40,000  pounds  per 
square  inch  (2812  kilogrammes  per  square  centimetre),  some 
so-called  wrought-irons  (properly  puddled  steels)  have  been  met 
with  by  the  Author  in  the  market  having  a  tenacity  of  double 
that  figure ;  some  samples  extend  25  per  cent  before  breaking, 
while  others,  with  similar  shape  and  size  of  test-piece  are  found 
nearly  as  brittle  as  cast-iron. 

Cast-iron  varies  in  tenacity  from  as  low  as  10,000  pounds 
per  square  inch  (703  kilogrammes  per  square  centimetre)  to 
more  than  50,000  pounds  (3515  kilogrammes  per  square  centi- 
metre) ;  while  metals  are  sold  under  the  name  of  "  steel "  hav- 
ing tenacities  varying  from  that  of  wrought-iron  up  to  over  100 
tons  per  square  inch  (15,746  kilogrammes  per  square  centi- 
metre). 

In  the  examples  of  results  of  tests  of  iron  and  steel  which 
will  be  hereafter  given,  therefore,  the  character  of  the  metal 
tested  will  usually  be  exactly  defined  by  its  chemical  composi- 
tion. 

In  comparing  the  results  of  test  with  the  chemical  constitu- 
tion of  the  material,  it  will  be  found  that,  in  general,  elements 
which  increase  tenacity  also  decrease  ductility  and  resilience. 

Thus :  carbon  increases  strength  up  to  a  limit  beyond  which 
an  excess  begins  to  weaken  it,  as  at  the  limit  which  separates 
steel  from  cast-iron ;  but  every  addition  of  strength  takes  place 
at  the  sacrifice  of  that  ductility  which  is  an  essential  property 
of  good  iron. 

Phosphorus  adds  strength,  as  do  manganese  and  other  less 
common  constituents ;  but  in  each  case  a  limit  to  increasing 
strength  is  reached,  and  in  each  case  the  increase  of  strength 
noted  is  accompanied  by  an  equally  or  more  noticeable  loss  of 
ductility.  It  sometimes  happens,  however,  that  the  elastic  re- 
silience increases,  with  addition  of  such  elements,  up  to  a  limit ; 
which  limit  is,  however,  reached  long  before  the  increase  of 
strength  ceases. 

The  influence  of  the  most  common  hardening  elements  upon 
the  valuable  qualities  of  "  rail-steel  "  and  similar  metals  has  not 
been  studied  sufficiently  to  determine  their  precise  effect  and 
their  modifying  action  as  mutually  reacting  upon  each  other. 


MATERIALS— STRENGTH  OF   THE   STRUCTURE.  6 1 

The  hardening  elements  most  usually  met  with  in  iron  and 
steel  are  carbon,  silicon,  manganese,  and  phosphorus.  Dr. 
Dudley*  takes  the  effect  of  manganese,  carbon,  silicon,  and 
phosphorus  to  be  as  the  numbers  3,  5,  7^,  and  15,  and  reckons 
the  sum  of  their  effects  in  "  phosphorus  units"  on  this  basis, 
allowing  0.05,  0.03,  0.02,  and  o.oi  per  cent  respectively  of  these 
elements,  taken  in  the  order  just  given,  as  each  equivalent  to 
one  unit.  He  concludes  that  the  sum  should  not  exceed  31  or 
32  in  rails  and  other  soft  ingot-metals,  this  figure  being  obtained, 
as  above,  by  adding  together  the  phosphorus  percentage,  one 
half  the  silicon,  one  third  the  carbon,  and  one  fifth  the  manga- 
nese. Taken  singly,  the  limit  for  phosphorus  is  placed  at  a 
maximum  of  o.io  per  cent,  silicon  at  0.04,  manganese  at  0.30  or 
0.40,  and  for  such  metals,  carbon  at  0.25  to  0.30  per  cent. 
Higher  proportions  make  the  material  too  brittle  for  rails  and 
similar  uses.  For  boiler-place  these  elements  should  be  re- 
duced nearly  one  half. 

Steels  containing  more  carbon  are  still  more  carefully  chosen 
with  a  view  to  the  avoidance  of  the  loss  of  ductility  due  to  the 
action  of  other  elements  in  presence  of  carbon. 

Manganese  steels,  i.e.,  steels  containing  a  high  percentage 
of  manganese,  having  but  little  carbon  or  other  of  the  harden- 
ing elements,  are  found  to  have  peculiar  value  for  many  purpo- 
ses of  construction  ;  but  their  use  must  be  carefully  avoided  in 
steam-boilers,  or  elsewhere,  when  exposed  to  great  and  rapid 
changes  of  temperature. 

The  chemical  composition  of  cast-iron  will  usually,  and  es- 
pecially if  checked  by  a  determination  of  density,  serve  well  as 
a  guide  to  the  selection  of  iron  of  any  specified  character  for  use 
in  construction ;  yet  it  is  always  advisable  to  supplement  the 
analysis  by  the  determination  of  its  physical  characteristics  as 
revealed  by  inspection  and  by  test.  The  openness  or  closeness 
of  grain,  the  shade  of  color,  the  depth  of  chill,  and  other  prop- 
erties capable  ot  detection  by  the  senses,  are  valuable  guides  to 
the  experienced  engineer. 

The  same  is  true  of  all  forms  of  ingot  metal,  whether  worked 


*  Trans.  Am.  Inst.  Mining  Engineers,  vol.  vii 


62  THE   STEAM-BOILER. 

or  unworked.  Steels  are  selected  by  visual  inspection  with 
great  accuracy  and  certainty ;  but  the  engineer  usually  desires  to 
compare  the  chemist's  analysis  with  the  results  of  mechanical 
tests,  as  well  as  to  obtain  the  judgment  of  the  steel-maker  who 
inspects  the  topped  ingots. 

The  products  of  the  pneumatic  and  of  the  open-hearth  pro- 
cesses are  now  customarily  tested  both  by  the  chemist's  and  by 
physical  tests. 

The  influence  of  mechanical  treatment  during  the  process 
of  manufacturing  wrought-iron  and  puddled  steel — the  "  weld  " 
metals — is  very  great  in  the  modification  of  their  valuable 
properties.  This  is  the  case  to  such  an  extent  that  the  quality 
of  these  materials  can  but  rarely  be  safely  judged  from  chemi- 
cal analysis.  The  presence  or  absence  of  cinder,  the  amount  of 
reduction  in  the  rolls  or  under  the  hammer,  and  the  tempera- 
ture and  other  conditions  of  working  are  circumstances  that 
modify  quality  to  such  an  extent  as  usually,  with  the  better 
kinds  of  metal,  to  entirely  obscure  variations  due  to  accidental 
differences  in  chemical  constitution  ;  with  other  irons  and  steels 
both  sets  of  conditions  concur  to  determine  quality.  It  is  never 
safe,  therefore,  to  base  specifications  for  these  materials  upon 
chemical  composition  alone  ;  actual  test  is  usually  demanded  as 
a  basis  for  their  acceptance  or  rejection. 

Cast-iron  has  some  advantages  as  a  material  for  steam-boil- 
ers, such  as  its  durability  in  presence  of  corroding  elements,  its 
freedom  from  liability  to  rapid  solution  by  acids,  its  compact 
structure  and  the  impossibility  of  becoming  laminated  ;  and  it 
is  found  to  have  practically  equal  conducting  power.  Its  cost 
is  also  low ;  but  it  is  exposed  to  danger  of  cracking,  either  from 
shrinkage  strains  or  local  variations  of  temperature ;  it  gives  no 
warning  when  such  danger  arises,  but  is  always  treacherous  and 
unreliable.  Its  composition  is  a  matter  of  uncertainty,  and  is 
never  absolutely  known.  The  cast-iron  boilers  are  usually  so 
constructed  that  it  is  easy  to  substitute  a  new  piece  for  a  broken 
part,  and  the  boiler  is  then  as  good  as  when  new,  instead  of 
being  weakened  by  the  operation,  as  is  apt  to  be  the  case  with 
wrought-iron  boilers.  On  the  other  hand,  they  are  considered 
to  be  commonly  somewhat  defective  in  circulation,  as  a  rule, 


MATERIALS— STRENGTH  OF    THE   STRUCTURE.  63 

and  deficient  in  steam-space.  Cast-steel  is  now  often  substi- 
tuted for  cast-iron  in  such  boilers,  and  is  at  once  stronger  and 
more  trustworthy ;  it  is  subject  to  the  same  objection  as  cast- 
iron  in  the  difficulty  met  with  in  securing  sound  castings. 
Could  good  castings  be  relied  upon  and  shrinkage  cracks  and 
strain  cracks  be  prevented,  the  material  would  undoubtedly  be 
much  more  generally  employed,  especially  in  small  boilers. 

•  32.  Steel  for  Boilers  is  always  of  the  class  known  as  "  low," 
41  soft,"  or  "  mild  "  steel,  and  is,  properly  speaking, "  ingot  iron  ;" 
all  erf  its  characteristics  being  those  of  a  homogeneous,  tena- 
cious, and  ductile  iron,  and  quite  distinct  from  those  of  the 
true  steels.  As  compared  with  iron,  its  greater  tenacity,  per- 
mitting the  use  of  thinner  sheets  for  a  given  pressure,  or  giving 
a  greater  margin  of  safety;  its  greater  homogeneousness,  in- 
suring more  certainty  and  security  in  attaining  the  conditions 
prescribed  in  designing;  and  its  greater  ductility,  which  adds 
enormously  to  the  safety  of  the  structure  against  dangerous 
strains  and  alterations  of  form :  all  make  it,  when  of  good  qual- 
ity, much  the  more  desirable  material.  It  is  rapidly  supersed- 
ing iron  in  boiler-construction.  The  difficulties  which  have 
retarded  its  introduction  have  been  mainly  those  of  getting 
perfect  uniformity  of  composition,  not  only  in  successive  lots, 
but  also  in  different  parts  of  the  same  lot,  and  even  in  the  same 
sheet.  Many  manufacturers  have  now  become  able  to  secure 
all  the  uniformity  desirable,  and  to  guarantee  the  quality  of 
their  product ;  from  them  good  boiler-plate  can  always  be  ob- 
tained. 

Steel  boiler-plate  is  usually  made  by  the  Siemens-Martin  or 
"open-hearth"  process;  although  considerable  quantities  are 
produced  from  the  Bessemer  converter,  and  some  by  the  more 
costly  crucible  process.  The  former  possesses  peculiar  advan- 
tages in  the  making  of  "  mild  "  steels  and  boiler-plate  in  conse- 
quence of  the  facility  which  it  offers  for  testing  the  quality  of 
the  metal  from  time  to  time,  while  still  molten  on  the  furnace- 
hearth,  and  then,  if  it  proves  not  to  be  of  the  desired  character, 
modifying  it,  by  addition  of  such  material  as  may  serve  to  im- 
prove it,  until  the  required  quality  is  obtained.  While  the 
Bessemer  process  in  skilled  hands  has  produced  most  excellent 


64  THE   STEAM-BOILER. 

steel,  very  uniform  in  grade,  neither  it  nor  the  crucible  process 
offers  such  facilities  for  test  and  adjustment  of  quality  as 
characterize  the  Siemens-Martin  system. 

The  composition  of  good  steel  boiler-plate  should  always 
be  such  as  will  give  great  ductility  and  perfect  freedom  from 
liability  to  harden  and  "  take  a  temper"  in  consequence  of 
variations  of  temperature  occurring  while  in  use.  The  carbon 
should  be  less  in  amount  than  one  fourth  of  one  per  cent,  and 
it  is  often  less  than  one  tenth.  Manganese,  which  usually  con- 
stitutes an  important  element,  should  be  as  low  as  is  possible 
consistent  with  soundness  and  homogeneousness.  Any  boiler- 
plate that,  on  being  heated  to  a  red-heat  and  suddenly  cooled, 
is  found  to  harden  perceptibly,  should  be  rejected.  It  should 
weld  readily,  and  should  be  capable  of  sustaining  all  the  tests 
customarily  demanded  of  boiler-iron  even  more  satisfactorily 
than  the  latter.  Its  ductility  should  be  greater  than  that  of 
iron. 

As  ordinarily  made,  steel  is  rarely  as  easily  manipulated,  and, 
when  subjected  to  the  ordinary  operations  of  boiler-making, 
seldom  exhibits  as  little  loss  of  quality  as  the  best  irons ;  it 
must  often  be  very  carefully  treated,  and  even  in  many  cases 
must  be  annealed  after  each  operation  to  restore  lost  ductility. 
Shearing  and  punching  steels  too  high  in  carbon,  or  containing 
too  much  manganese  or  phosphorus,  is  very  certain  to  produce 
injury. 

33.  The  Effect  of  Variation  of  Form  of  a  piece  of  metal, 
a  member,  or  a  structure,  is  often  extremely  important.  This 
generally  so  considerably  modifies  the  apparent  tenacity  of 
iron  and  steel  that  it  is  necessary  to  note  the  size  and  shape 
of  the  specimen  tested  before  an  intelligent  understanding  of 
the  value  of  the  material  can  be  arrived  at  by  examination  of 
data  secured  by  test.  When  a  piece  of  metal  is  subjected  to 
stress  and  slowly  pulled  asunder,  it  will  yield  at  the  weakest 
section  first ;  and  if  that  section  is  of  considerably  less  area  than 
adjacent  parts  (Fig.  48),  or  if  the  metal  is  not  ductile,  it  will 
often  break  sharply,  and  without  stretching  appreciably,  as  seen 
in  Fig.  50 ;  the  fractured  surface  will  have  a  granular  appearance, 
and  the  behavior  of  the  piece,  as  a  whole,  may  be  like  that  of  a 


MATERIALS— STRENGTH  OF    THE    STRUCTURE.  65 

brittle  casting,  even  although  actually  made  of  tough  and  duc- 
tile metal,  when  the  piece  is  deeply  scored. 

When  a  bar  of  very  ductile  metal,  of  perfectly  uniform  cross- 
section  (Fig.  49)  is  broken,  on  the  other  hand,  it  will,  at  first,  if 
of  uniform  quality,  gradually  stretch  with  a  nearly  uniform 
reduction  of  section  from  end  to  end.  Toward  the  ends,  where 
held  by  the  machine,  this  reduction  of  area  is  less  perceivable, 
and  on  the  extreme  ends,  where  no  strain  can  occur,  except  from 
the  compressing  action  of  the  grips,  the  original  area  of  section 


FIG.  48.— Incorrect.  FIG.  49.— Correct. 

FORMS  OF  TEST-PIECES  FOR  TENSION. 


is  retained,  diminution  taking  place  from  that  point  to  the  most 
strained  part  by  a  gradual  taper  or  by  a  sudden  reduction  of 
section,  according  to  the  method  adopted  of  holding  the  rod. 
When  the  stress  has  attained  so  great  an  intensity  that  the 
weakest  section  is  strained  beyond  its  elastic  limit,  "  flow " 
begins  there,  and,  while  the  extension  of  other  parts  continues 
slowly,  the  portions  immediately  adjacent  to  the  overstrained 
section  stretch  more  and  more  rapidly  as  this  local  reduction 
of  section  continues,  and  finally  fracture  takes  place.  This 
locally  reduced  portion  of  the  rod  has  a  length  which  is  depend- 
ent upon  the  character  of  the  metal  «and  the  size  of  the  piece. 
5 


66 


THE   STEAM-BOILER. 


Hard  and  brittle  materials  exhibit  very  little  reduction,  and 
the  reduced  portion  is  short,  as  in  Fig.  50: 
ductile  and  tough  metals  exhibit  a  marked  re- 
duction over  a  length  of  several  diameters,  and 
great  reduction  at  the  fractured  section,  as  seen 
in  Fig.  51.  Of  the  samples  shown  in  the  figures, 
the  first  is  of  a  good,  but  a  badly  worked,  iron, 
and  the  secon.d  from  the  same  metal  after  it 
had  been  more  thoroughly  worked. 

When  the  breaking  section  is  determined  by 
deeply  grooving  the  test-piece,  the  results  of  test 
are  higher  by  5  or  10  per  cent  than  when  the 
cylinders  are  not  so  cut,  if  the  metal  is  hard  and 
brittle,  and  by  20  to  25  per  cent  with  tough 
and  ductile  irons  or  steels.  In 
ordinary  work  this  difference  will 
average  at  least  20  per  cent  with 
the  ductile  metals.  A  good 
bridge  or  cable  iron  in  pieces  of 
i  inch  (2.54  centimetres)  diame- 
ter cut  from  2-inch  (5.08  centi- 
metres) bar,  exhibited  a  tenacity  of  50,000 
pounds  per  square  inch  in  long  test-pieces, 
and  60,000  in  short  grooved  specimens  (3515 
to  4218  kilogrammes  per  square  centimetre). 
Cast-irons  will  give  practically  equal  results  by 
both  tests,  as  will  hard  steels  and  very  coarse- 
grained hard  wrought  irons. 

Since  these  differences  are  so  great  that  it 
is  necessary  to  ascertain  the  form  of  samples 
tested  before  the  results  of  test  can  be  properly 
interpreted,  it  becomes  advisable  to  use  a  test- 
piece  of  standard  shape  and  size  for  all  tests  the 
results  of  which  are  to  be  compared.  The  fig- 
ures given  hereafter,  when  not  otherwise  stated, 
may  be  assumed  to  apply  to  pieces  of  one  half 
square  inch  area  (3.23  square  centimetres)  of  FIG.  5i. 
section,  and  at  least  5  diameters  in  length.  This  length  is 


FIG.   50. 


MATERIALS—  STRENGTH   OF    THE   STRUCTURE.  6/ 

usually  quite  sufficient,  and  is  taken  by  the  Author  as  a  mini- 
mum. For  other  lengths,  the  extension  is  measured  by  a  con- 
stant function  of  the  total  length  plus  a  function  of  the  diame- 
ter, which  varies  with  the  quality  of  the  metal  and  the  shape 
of  the  test-piece.  It  may  be  expressed  by  the  formula 

e  =  al+f(d)  ........     (i) 

The  elongation  often  increases  from  20  up  to  40  per  cent 
as  the  test-piece  is  shortened  from  5  inches  (12.7  centimetres) 
to  -J  inch  (1.27  centimetres)  in  length,  while  the  contraction  of 
section  is,  on  the  other  hand,  decreased  from  50  down  to  25  per 
cent,  nearly.  Fairbairn,*  testing  good  round  bar-iron,  found 
that  the  extension  for  lengths  varying  from  10  inches  (25.4 
centimetres)  to  10  feet  (3.28  metres)  could  be  expressed,  for 
such  iron,  by  the  formula 

'  =  18  +  7,      .......     (2) 

where  /  is  the  length  of  bar  in  inches.  In  metric  measures  this 
becomes 


/  =  length  in  centimetres  ;  e  =  elongation  per  unit  of  length. 

This  influence  of  form  is  as  important  in  testing  soft  steels  as 
in  working  on  iron.  Col.  Wilmot,  testing  Bessemer  "steel"  at 
the  Woolwich  Arsenal,  G.  B.,  obtained  the  following  figures: 

TENACITY. 

FORM.              TEST-PIECE.                        Lbs.  per  sq.  in.  Kilogs.  per  sq.  cm. 

Grooved,  Fig.  48,  Highest  ............     162,974  n,457 

Lowest  .............     136,490  9,595 

Average  ...........     I53>6?7  10,803 

Long  cylinder  ----  Highest  ............     123,165  8,658 

Lowest  .............     103,255  7-259 

Average  ............      114,460  8,047 

*  Useful  Information,  second  series,  p.  301. 


68 


THE   STEAM-BOILER, 


The  difference  amounts  to  between   30  and   35   per  cent,  the 
groove  giving  an  abnormally  high  figure. 

It  is  evident  from  the  above  that  the  elongation  must  be 
proportionably  much  greater  in  short  specimens  than  in  long 
pieces.  This  is  well  shown  below  in  tests  made  by  Capt. 
Beardslee  for  the  United  States  Board.* 

TESTS  OF  TEST-PIECES  OF  VARYING  PROPORTIONS-TENSION. 


rt 

, 

STRESS  WHEN 

DIAME- 

g 

PIECE  BEGAN 

BREAKING- 

"* 

o 

TER. 

C    • 

TO    STRETCH 

STRESS. 

5 

uS 

OBSERVABLY. 

"o 

<rt<*1 

Remarks. 

ji 

s 

Orig- 
inal. 

Final. 

'er  cent 
tion. 

g 

c 

deduced. 

'ercent  < 
tion  of 

Ob- 
served 
Stress. 

Stress 
per 
square 
inch. 

Ob- 
served 
Stress. 

Stress 
per 
square 
inch. 

^ 

PM 

o 

H 

M 

In. 

In. 

In. 

In. 

Lbs. 

Lbs. 

Lbs. 

Lbs. 

I 

5.000 

6.522 

30.0 

-798 

.568 

49-3 

13.400 

26,800 

26,000 

51.989 

Elastic  limit,  26,795  Ibs. 

per  sq.  in. 

2 

3-938 

5-204 

32.0 

.798 

-564 

50.0 

14,000 

28,000 

26,200 

52,389 

Elastic  limit,  28,194  Ibs. 

per  sq.  in. 

3 

4-500 

5.853 

30.0 

•797 

-584 

46-3 

14,000 

28,290 

26,190 

52,495 

Elastic  limit,  28,062  Ibs. 

per  sq.  in. 

4 

3-500 

4.605 

31-6 

.791 

•57° 

48.0 

13,000 

26.450    26,070 

53,052 

Elastic  limit,  27,268  Ibs. 

per  sq.  in. 

5 

3.000 

3-977 

33-o 

.792 

•571 

48.0 

14.000 

28.420    26,100 

52.984 

6 

2.472 

3.266 

32.1 

•799 

•589 

45-6 

14,000 

27,920 

26.500 

52.852 

7 

1.989 

2.644 

32-9 

.798 

•591 

45-° 

14,000 

28,000 

26,500 

53.169 

8 

i  .500 

2.026 

35-0 

•797 

•590 

45-2 

15.500 

31,320 

26,275 

52,666 

9 

I.OOO 

1-354 

35-4 

.798 

.600 

43-5 

16,675 

33,350 

26,590 

53,169 

10 

o.  500 

0.708 

41.6 

.798 

.635 

36.6 

18,760 

37,520 

.28,665 

57,3^8 

With  such  brittle  materials  as  the  cast-irons,  the  difference 
becomes  unimportant.  Beardslee  found  a  difference  of  but  I 
per  cent  in  certain  cases.  The  more  brittle  the  material  the  less 
this  variation  of  the  observed  tenacity. 

As  will  be  seen  later,  even  more  important  variations  follow 
changes  of  proportion  of  pieces  in  compression.  No  test-piece 
should  be  of  very  small  diameter,  as  inaccuracy  is  more 
probable  with  a  small  than  with  a  large  piece,  and  the  errors 
are  more  likely  to  be  increased  in  reduction  to  the  stress  per 
square  inch.  The  length  should  not  be  less  than  four  times  the 
diameter  in  any  case,  and  with  soft  ductile  metal  five  or  six 
diameters  would  be  preferable,  for  tension. 


Report,  p.  104. 


MATERIALS— STRENGTH  OF    THE   STKUCTUKE. 


69 


Where  much  work  is  to  be  done,  it  is  quite  important  that 
a  set  of  standard  shapes  of  test-pieces  should  be  selected,  and 
that  all  the  tests  should  be  made  upon  samples  worked  to 
standard  size  and  form.  Thus,  tension-pieces  are  often  made 
of  the  shapes  seen  in  the  figure,  when  testing  square,  cylindrical, 
or  flat  samples,  or  samples  cut  from  the  solid.  The  last  is  a 
shape  called  for  under  the  U.  S.  inspection  laws  when  testing 
boiler-plate ;  but  it  should  never  be  used  if  choice  is  permitted, 
as  it  gives  no  chance  of  stretching,  and  is  therefore  nearly  use- 
less as  a  gauge  of  the  quality  of  the  metal ;  it  will  undoubtedly 
be  abandoned  in  course  of  time,  as  it  invariably  gives  too  high  a 
figure,  and  does  not  distinguish  the  hard  and  brittle  from  the 
better  and  tougher  materials  which  are  desired  in  construction. 

The  dimensions  adopted  by  the  Author  are  one-half  square 
inch  (3. 23  square  centimetres)  section  for  all  metals  except  the 


.16  T0201 


FIG.  52. — SHAPES  FOR  TEST-PIECES. 

tool  steels  (0.798  inch ;  2  centimetres  diameter  when  round), 
and  one-eighth  or  one-quarter  square  inch  (0.8 1  to  1.61  square 
•centimetres  area ;  0.398  or  0.565  inch,  I  or  1.4  centimetres  diame- 
ter) for  the  latter,  at  the  smallest  cross-section.  Kent,  who  sketches 
the  above,  takes  these  shapes,  making  them,  if  of  tool  steel,  ^ 
inch  diameter  (1.75  centimetres),  or  f  square  inch  (2.44  square 
centimetres)  area ;  in  other  metals  either  £  inch  (1.9  centimetres) 


7O  THE   STEAM-BOILER. 

diameter  or  0.44  square  inch  (2.84  square  centimetres),  or  as 
above.  The  edges  should  be  true  and  smooth,  and  the  fillets  % 
inch  radius. 

For  compression  tests  of  metal,  I  inch  (2.54  centimetres) 
long  and  \  inch  (1.27  centimetres)  diameter,  ends  perfectly 
square,  is  recommended  ;  for  stone  and  brick,  a  2-inch  (5.08 
centimetres)  cube.  Transverse  test-pieces  should  not  be  less 
than  i  foot  nor  more  than  4  feet  in  length,  when  to  be  handled 
in  ordinary  machines. 

The  standard  specimen  will  be  taken  as  above,  and  good 
wrought-iron  of  such  shape  and  size  should  exhibit  a  tenacity 
of  at  least  50,000  pounds  (3515  kilograms  per  square  centimetre) 
if  from  bars  not  exceeding  2  inches  (5.08  centimetres)  diameter,, 
and  should  stretch  25  per  cent  with  40  per  cent  reduction  of 
area.  Such  test-pieces  have  the  advantage  of  giving  uniform 
comparable  and  minimum  figures  for  tenacity,  and  of  permitting 
accurate  determinations  of  elongation. 

Test-pieces  are  only  satisfactory  in  form  when  turned  in 
the  lathe,  as  the  coincidence  of  the  central  line  of  figure  with 
the  line  of  pull  is  thus  most  perfectly  insured.  When,  as  with 
sheet-metal,  this  cannot  be  done  readily,  care  must  be  taken  to 
secure  proportions  of  length  and  cross-section  as  nearly  like 
those  of  the  standard  test-piece  as  possible,  and  to  secure  sym- 
metry and  exactness  of  form  and  dimension ;  such  pieces  are 
liable  to  yield  by  tearing  when  not  well  made  and  properly 
adjusted  in  the  machine. 

34.  The  Method  of  Treatment  of  metal,  either  previous 
to  its  use  in  any  structure  or  while  under  load,  often  seriously 
modifies  its  strength,  its  ductility,  and  its  endurance. 

Bar-irons  exhibit  a  wide  difference  of  strength,  due  ta 
difference  of  section  alone.  This  variation  may  be  expressed 
approximately  with  good  irons,  such  as  the  Author  has  studied 
in,  this  relation,  by  the  formulas 

T  =  56,000  —  20,000  log  d\  \  , 

Tm  —    4,500  —    i, 406 log  dm.  } 

Where  T  and  Tm  measure  the  tenacity  in  British  and  metric 


MATERIALS— STRENGTH  OF    THE    STRUCTURE. 


measures  respectively,  and  d  and  dm  the  diameter  of  the  piece, 
or  its  least  dimension. 

Where  it  is  desired  to  use  an  expression  which  is  not  loga- 
rithmic, it  will  usually  be  safe  to  adopt  in  specifications  the 
following : 


_ 

y  : 


60,000 


80,000 


The  Edgemoor  Iron  Company  adopt,  for  wrought-iron  in 
tension,  the  formula 

7,000^4 
T  =  52,000  -  '—— , 


in  which  A  is  the  area,  and  B  the  periphery  of  the  section.* 

The '  figures  in  the  following  table  have  been  taken  by  the 
Author  as  fair  values  of  the  tenacity  of  good  average  merchant- 
iron. 

TENACITY    OF    GOOD    IRON. 


DIAMETER. 

TENACITY,  T. 

Centimetres. 

Inches. 

Lbs. 
per  square  inch. 

Kilogrammes 
per  square  inch. 

.64 

i 

6o,OOO 

4.218 

1.27 

* 

58,000 

4,077 

I.QO 

f 

56,000 

3.947 

2.54 

I 

55,500 

3,902 

3-18 

Ii 

54,500 

3,838 

3.8i 

Ii 

53,500 

3,761 

4-45 

If 

52.000 

3,656 

5-o8 

2 

50,000 

3.515 

5-72 

2i 

49,OOO 

3-445 

6.35 

2i 

48,900 

3-374 

7.62 

3 

47-500 

3-320 

8.90 

3i 

47,OOO 

3,304 

10.  16 

4 

46,000 

3.234 

12.  7O 

5 

44,000 

3.093 

Kirkaldyf  found    that   pieces  of  1 1-inch  (3.2   centimetres) 


*  Ohio  Railway  Report,  1881,  p.  379. 

f  Experiments  on  Wrought  Iron  and  Steel. 


72  THE   STEAM-BOILER. 

bar  rolled  down  to  I  inch  (2.54  centimetres),  f  inch  (1.9  centi- 
metres), and  -J  inch  (1.27  centimetres)  diameter  increased  in 
tenacity  20  per  cent  while  decreasing  in  ductility  5  per  cent. 

Forging  has  the  same  effect  as  rolling. 

The  elastic  limit  is  also  usually  lower  in  large  than  in  small 
masses. 

Turning  iron  down  has  no  important  effect  on  the  tenacity. 
The  considerable  variations  always  observable  in  the  gen- 
eral rate  of  increase  of  tenacity,  which,  other  things  being 
equal,  accompanies  reduction  of  size  of  wire,  are  due  to  the 
hardening  of  the  wire  in  the  draw-plate,  and  occasional  restora- 
tion to  its  softest  condition  by  annealing. 

Beardslee  has  found  the  change  of  tenacity  in  forged  and 
rolled  bars  to  be  due  to  differences  in  amount  of  work  done  in 
the  mill  upon  the  iron.  The  extent  of  reduction  of  the  pile 
sent  to  the  rolls  from  the  heating-furnace  is  variable,  its  cross- 
sectional  area  being  originally  from  20  to  60  times  that  of  the 
bar,  the  higher  figure  being  that  for  the  smallest  bars.  On 
making  this  reduction  uniform,  it  is  found  that  the  tenac- 
ity of  bars  varies  much  less  in  different  sizes,  and  that  the 
change  becomes  nearly  uniform  from  end  to  end  of  the  series 
of  sizes,  and  becomes  also  very  small  in  amount.  By  properly 
shaping  the  piles  at  the  heating-furnace,  and  by  putting  as 
much  work  on  large  as  on  small  bars,  it  was  found  that  a  2-inch 
(5.08  centimetres)  bar  could  be  given  a  strength  superior  by 
over  10  per  cent,  and  a  4-inch  (10.17  centimetres)  could  be 
made  stronger  by  above  20  per  cent  than  iron  of  those  sizes  as 
usually  made  for  the  market.  The  surface  of  a  bar  is  usually 
somewhat  stronger  than  the  interior. 

The  Limit  of  Elasticity  will  be  found  at  from  two  fifths 
the  ultimate  strength  in  soft,  pure  irons  to  three  fifths  in 
harder  irons,  and  from  three  fifths  in  the  steels  to  nearly  the 
ultimate  strength  with  harder  steels  and  cast-irons.  Barlow 
found  good  wrought-iron  to  elongate  one  ten-thousandth  its 
length  per  ton  per  square  inch  up  to  the  limit  at  about  10 
tons.  The  relation  between  the  series  of  elastic  limits  and  the 
maximum  resistance  of  the  iron  or  the  steel  is  well  shown  in 
strain-diagrams,  which  exhibit  graphically  the  varying  relation 


MATERIALS— STRENGTH   OF    THE    STRUCTURE.  73 

of  the  stress  applied  to  the  strain  produced  by  it  throughout 
the  process  of  breaking. 

Repeatedly  Piling  and  Reworking  improves  the  quality  of 
wrought-iron  up  to  a  limit  at  which  injury  is  done  by  over- 
working and  burning  it. 

The  iron  thus  treated  exhibits  increasing  strength  until  it 
has  been  reheated  five  or  six  times,  and  then  gradually  loses 
tenacity  at  a  rate  which  seems  to  be  an  accelerating  one. 
Forging  iron  is  similar  in  effect,  and  improves  the  metal  up  to 
a  limit  seldom  reached  in  small  masses. 

The  forging  of  large  masses  usually  includes  too  often  re- 
peated piling  and  welding  of  smaller  pieces,  and  it  is  thence 
found  difficult  to  secure  soundness  and  strength.  This  is  par- 
ticularly the  case  where  the  forging  is  done  with  hammers  of 
insufficient  weight.  The  iron  suffers,  not  only  from  reheating, 
but  from  the  gradual  loosening  and  weakening  of  the  cohesion 
of  the  metal  within  the  mass  at  depths  at  which  the  beneficial 
effect  of  the  hammer  is  not  felt. 

The  Effect  of  Prolonged  Heating  is  sometimes  seen  in  a 
granular,  or  even  crystalline,  structure  of  the  iron,  which  indi- 
cates serious  loss  of  tenacity.  Large  masses  must  always  be 
made  with  great  care,  and  used  with  caution  and  with  a  high 
factor  of  safety.  Ingot  iron  is  always  to  be  preferred  to  welded 
masses  of  forged  material  for  shafts  of  steamers  and  similar 
uses. 

The  Tenacity  of  Ingot  Irons  and  Steels  is  less  subject  to 
variation  by  accidental  modifications  of  structure  and  compo- 
sition than  is  that  of  wrought-iron.  The  steels  are  usually 
homogeneous  and  well  worked,  and  are  comparatively  free 
from  objectionable  elements,  their  variation  in  quality  being 
determined  principally  by  the  amount  of  carbon  present,  which 
element  occurs  in  a  proportion  fixed  by  the  maker,  and  varying 
within  a  very  narrow  range.  The  softest  grades  of  ingot  iron 
and  steel  approach  the  character  of  wrought-irons ;  but  their 
comparative  freedom  from  slag,  and  their  purity,  usually  make 
them  superior  to  all  ordinary  irons  in  combined  strength  and 
ductility.  The  products  of  the  Bessemer  and  of  the  open- 
hearth  processes  vary  in  tenacity  from  60,000  pounds  per  square 


74  THE   STEAM-BOILER. 

inch  (4218  kilogrammes  per  square  centimetre)  to  more  than 
double  that  figure;  while  the  crucible  steels  often,  and  occa- 
sionally the  preceding,  are  sometimes  four  times  as  strong,  a 
tenacity  of  200,000  pounds  per  square  inch  (14,060  kilogrammes 
per  square  centimetre)  being  sometimes  exceeded. 

35.  The  Time  and  the  Margin  of  Stress,  or  loading, 
both  affect  greatly  the  life  of  the  piece  and  the  degree  of  safety 
with  which  it  may  be  used. 

It  has  been  shown  by  the  Author,  and  by  Commander 
Beardslee,  U.  S.  N.,  by  direct  experiment  in  the  Mechanical 
Laboratory  of  the  Stevens  Institute  of  Technology,  and  at  the 
Washington  Navy  Yard,  that  the  normal  elastic  limit,  as  ex- 
hibited on  strain-diagrams  of  tests  conducted  without  inter- 
mission of  stress,  is  exalted  or  depressed  when  intermission  of 
distortion  occurs,  according  as  the  metal  belongs  to  the  iron  or 
to  the  tin  class.  This  elevation  of  the  normal  elastic  limit  by 
intermitting  strain  is,  as  has  been  shown,  variable  in  amount 
with  different  materials  of  the  iron  class,  and  the  rate  at  which 
this  exaltation  progresses  is  also  variable.  With  the  same 
material  and  under  the  same  conditions  of  manufacture  and  of 
subsequent  treatment  the  rate  of  exaltation  is  quite  definite, 
and  may  be  expressed  by  a  very  simple  formula.  The  Author 
has  experimented  with  bridge  material,  and  Commander 
Beardslee  has  examined  metal  specially  adapted  for  use  in 
chain  cables,  for  which  latter  purpose  an  iron  is  required,  as  in 
bridge-building,  to  be  tough  as  well  as  strong  and  uniform  in 
structure  and  composition.  The  experiments  of  the  latter  in- 
vestigator have  extended  to  a  wider  range  than  have  those  of 
the  Author,  and  the  effect  of  the  intermission  of  strains  con- 
siderably exceeding  the  primitive  elastic  limit  has  been  deter- 
mined by  him  for  periods  of  from  one  minute  to  one  year. 
From  a  study  of  the  results  of  such  researches  and  from  a  com- 
parison with  the  latter  investigation,  which  was  found  to  be 
confirmatory  of  the  deduction,  the  Author  has  found  that,  with 
such  iron  as  is  here  described,  the  process  of  exaltation  of  the 
normal  elastic  limit  due  to  any  given  degree  of  strain  usually 
nearly  reaches  a  maximum  in  the  course  of  a  few  days  of  rest 
after  strain,  its  progress  being  rapid  at  first  and  the  rate  of  in- 


MATERIALS— STRENGTH  OF   THE   STRUCTURE. 


75 


crease  quickly  diminishing  with  time.  For  good  boiler  irons, 
the  amount  of  the  excess  of  the  exalted  limit,  as  shown  by  sub- 
sequent test,  above  the  stress  at  which  the  load  had  Seen  pre- 
viously removed  may  be  expressed  approximately  by  the 
formula 

E'  =  $  log  T-\-  1.50  per  cent ; 

in  which  the  time,  T,  is  given  in  hours  of  rest  after  removal  of 
the  tensile  stress  which  produced  the  noted  stretch. 

The  Author  has  investigated  the  action  of  prolonged  stress, 
using  wire  of  Swedish  iron :  but  one  set  of  samples  was  an- 
nealed ;  the  other,  of  two  sets,  was  left  hard,  as  drawn  from  the 
wire-blocks.  The  size  selected  was  No.  36,  0.004  inch  (o.oi 
millimetre)  diameter,  and  was  loaded  with  95,  90,  85,  80,  75, 
70,  65,  and  60  per  cent  of  the  breaking  load  as  obtained  by  the 
usual  method  of  test.  The  result  was : 

ENDURANCE    OF    IRON    WIRE    UNDER    STATIC    LOAD. 


TIME  UNDER 

LOAD  BEFORE  FRACTURE. 

PER  CENT  MAXIMUM 

STATIC  LOAD 

Hard  wire  (unannealed). 

Soft  wire  (annealed). 

95 

8  days. 

3  minutes. 

QO 

35  ^ays. 

5  minutes. 

85 

Unbroken  at  end  of  16 

mos. 

i  day. 

80 

91  days. 

266  days. 

75 
70 

!             Unbroken. 

j 

17  days. 

455  days. 

65 

( 

455  days. 

60 

Unbroken. 

Several  years. 

Soft  irons  and  the  "  tin  class"  of  metals  and  the  woods  are 
found  to  demand  a  higher  factor  of  safety  than  hard  iron.  The 
elegant  and  valuable  researches,  also,  of  Mons.  H.  Tresca  on 
the  flow  of  solids,*  and  the  illustrations  of  this  action  almost 
daily  noticed  by  every  engineer,  seem  to  lend  confirmation  to 
the  supposition  of  Vicat.  The  experimental  researches  of 
Prof.  Joseph  Henry,  on  the  viscosity  of  materials,  and  which 


*  Sur  1'Ecoulement  des  corps  solides.     Paris,  1869-72. 


76  THE   STEAM-BOJLER. 

proved  the  possibility  of  the  coexistence  of  strong  cohesive 
forces  with  great  fluidity,*  long  ago  proved  also  the  possibility 
of  a  behavior  in  solids,  under  the  action  of  great  force,  analo- 
gous to  that  noted  in  more  fluid  substances. 

On  the  other  hand,  the  researches  of  the  Author,  indicating 
by  strain-diagrams  that  the  progress  of  this  flow  is  often  ac- 
companied by  increasing  resistance,  and  the  corroboratory  evi- 
dence furnished  by  all  such  carefully  made  experiments  on 
tensile  resistance  as  those  of  King  and  Rodman,  Kirkaldy  and 
Styffe,  have  made  it  appear  extremely  doubtful  whether  hard 
iron  is  ever  weakened  by  a  continuance  of  any  stress  not  origi- 
nally capable  of  producing  incipient  rupture. 

Kirkaldy  concludes  that  the  additional  time  occupied  in 
testing  certain  specimens  of  which  he  determined  the  elonga- 
tion "  had  no  injurious  effect  in  lessening  the  amount  of  break- 
ing strain."  f  An  examination  of  his  tables  shows  those  bars 
which  were  longest  under  strain  to  have  had  highest  average 
resistance. 

Wertheim  supposed  that  greater  resistance  was  offered  to 
rapidly  than  to  slowly  produced  rupture. 

The  experiments  of  the  Author  prove  that,  as  had  already 
been  indicated  by  Kirkaldy,  a  lower  resistance  is  offered  by 
ordinary  irons  as  the  stress  is  more  rapidly  applied.  This  effect 
conspires  with  vis  viva  to  produce  rupture. 

We  conclude  that  the  rapidity  of  action  in  cases  of  shock, 
and  where  materials  sustain  live  loads,  is  a  very  important  ele- 
ment in  the  determination  of  their  resisting  power,  not  only 
for  the  reason  given  already,  but  because  the  more  rapidly 
common  iron  is  ruptured  the  less  is  its  resistance  to  fracture. 
This  loss  of  resistance  is  about  15  per  cent  \  in  some  cases, 
noted  by  the  Author,  of  moderately  rapid  distortion. 

The  cause  of  this  action  bears  a  close  relation  to  that 
operating  to  produce  the  opposite  phenomenon  of  the  ele- 
vation of  the  elastic  limit  by  prolonged  stress,  to  be  de- 

*  Proc.  Am.  Phil.  Society,  1844. 

f  Experiments  on  Wrought  Iron  and  Steel,  pp.  62,  83. 

\  Compare  Kirkaldy,  p.  83,  where  experiments  which  are  possibly  affected 
by  the  action  of  vis  viva  indicate  a  very  similar  effect. 


MATERIALS— STRENGTH  OF   THE   STRUCTURE.  ?? 

scribed,  and  it  may  probably  be  simply  another  illustration 
of  the  effect  of  internal  strain.  Metals  of  the  "  tin  class"  ex- 
hibit,  as  has  been  shown  by  the  Author,*  an  opposite  effect. 
Rapidly  broken,  they  offer  greater  resistance  than  to  a  static 
or  slowly  applied  load.  It  has  also  been  seen  that  annealed 
iron  has,  in  some  respects,  similar  qualities. 

With  a  very  slow  distortion  the  "  flow"  already  described 
occurs,  and  but  a  small  amount  of  internal  strain  is  produced, 
since,  by  the  action  noticed  when  left  at  rest,  this  strain  re- 
lieves itself  as  rapidly  as  produced.  A  more  rapid  distortion 
produces  internal  stress  more  rapidly  than  relief  can  take 
place,  and  the  more  quickly  it  occurs  the  less  thoroughly  can  it 
be  relieved,  and  the  more  is  the  total  resistance  of  the  piece 
reduced.  Evidence  confirmatory  of  this  explanation  is  found 
in  the  fact  that  bodies  most  homogeneous  as  to  strain  exhibit 
these  effects  least. 

At  extremely  high  velocities  the  most  ductile  substances 
exhibit  similar  behavior  when  fractured  by  shock  or  by  a  sud- 
denly applied  force,  to  substances  which  are  really  compara- 
tively brittle. f  In  the  production  of  this  effect,  which  has 
been  frequently  observed  in  the  fracture  of  iron,  although  the 
cause  has  not  been  recognized,  the  inertia  of  the  mass  attacked 
and  the  actual  depreciation  of  resisting  power  just  observed, 
conspire  to  produce  results  which  would  seem  quite  inexpli- 
cable, except  for  the  evidently  'great  concentration  of  energy 
here  referred  to,  which,  in  consequence  of  this  conspiring  of 
inertia  and  resistance,  brings  the  total  effort  upon  a  compara- 
tively limited  portion  of  the  material,  producing  the  short 
fracture,  with  its  granular  surfaces,  which  is  the  well-known 
characteristic  of  sudden  rupture.  Any  cause  acting  to  produce 
increased  density,  as  reduction  of  temperature,  evidently  must 
intensify  this  action  of  suddenly  applied  stress. 

The  liability  of  machinery  and  structures  to  injury  by 
shock  is  thus  greatly  increased,  and  it  is  quite  uncertain  what 


*  Trans.  Am.  Soc.  C.  E.,  1874  et  seq. 

\  Specimens  from  wrought-iron  targets  shattered  by  shock  of  heavy  ord- 
nance exhibit  this  change  in  a  very  unmistakable  manner. 


78  THE   STEAM-BOILER. 

is  the  proper  factor  of  safety  to  adopt  in  cases  in  which  the 
shocks  are  very  suddenly  produced. 

Meantime  the  precautions  to  be  taken  by  the  engineer  are : 
To  prevent  the  occurrence  of  shock  as  far  as  possible,  and  to 
use  in  endangered  parts  light  and  elastic  members,  composed 
of  the  most  ductile  materials  available,  giving  them  such  forms 
and  combinations  as  shall  distribute  the  distortion  as  uniformly 
and  as  widely  as  possible. 

The  behavior  of  materials  subjected  to  sudden  strain  is 
thus  seen  to  be  so  considerably  modified  by  both  internal  and 
external  conditions  which  are  themselves  variable  in  character, 
that  it  may  still  prove  quite  difficult  to  obtain  mathematical 
expressions  for  the  laws  governing  them.  An  approximation, 
of  sufficient  accuracy  for  some  cases  which  frequently  arise  in 
practice,  may  be  obtained  for  the  safety  factor  by  a  study  and 
comparison  of  experimental  results. 

Egleston,  studying  the  behavior  of  metal  under  long-con- 
tinued and  repeated  stresses,  finds  evidence  of  the  existence  of 
a  "  law  of  fatigue  and  refreshment  of  metals,"  occurring  as  in- 
dicated by  the  Author.  He  also  concludes*  that  metal  once 
fatigued  may  sometimes  be  restored  by  rest  or  by  heating 
that  "  the  change  produced  is  a  chemical  one,"  accompanied 
by  "  a  change  in  the  size,  color,  and  surface  of  the  grains  of  the 
iron  or  the  steel."  Surface  injuries  by  blows  were  found  to 
affect  the  metal,  in  some  cases,  to  a  depth  of  15  millimetres 
(0.6  inch).  He  informs  the  Author  that  he  finds  evidence  of 
the  formation  of  crystals  in  the  cold  metal  during  the  process 
of  becoming  fatigued,  and  a  decided  change  in  the  proportion 
of  combined  and  uncombined  carbon. 

The  Effect  of  Repeated  Variation  of  Load  is  most  important. 
In  the  year  1859  Pr°f*  Wohler,  in  the  employ  of  the  German 
Government,  undertook  a  series  of  experiments  to  determine 
the  effect  of  prolonged  varying  stress  on  iron  and  steel.  These 
experiments  were  continued  until  1870.  The  apparatus  used 
by  Wohler  and  his  successor,  Spaiigenberg,  was  of  four  kinds : 

I.  To  produce  rupture  by  repeated  load. 

*  Transactions  Institute  Mining  Engineers,  1880. 


MATERIALS— STRENGTH   OF    THE   STRUCTURE.  ?$ 

2.  For   repeated   bending,    in    one   direction,  of   prismatic 
rods. 

3.  For  experiments  on  loaded  rods  under  constant  bend- 
ing stress. 

4.  For  torsion  by  repeated  stress. 

The  amount  of  the  imposed  stress  was  determined  by 
breaking  several  rods  of  like  material,  ascertaining  the  break- 
ing load,  and  taking  some  fraction  of  this  for  the  intermittent 
load. 

From  the  results  of  these  experiments  of  Wohler,  extend- 
ing over  eleven  years,  the  observations  here  appended  were 
deduced  : 

"  WOHLER'S  LAW  :  Rupture  of  material  may  be  caused  by 
repeated  vibrations,  none  of  which  attain  the  absolute  breaking 
limit.  The  differences  of  the  limiting  strains  are  sufficient  for 
the  rupture  of  the  material" 

The  number  jf  strains  required  for  rupture  increases  much 
more  rapidly  than  the  weight  of  load  diminishes. 

The  work  of  Wohler  and  Spangenberg  has  proven  what 
was  long  before  supposed  to  be  the  fact — that  the  permanence 
and  safety  of  any  iron  or  steel  structure  depends  not  simply 
on  the  greatest  magnitude  of  the  load  to  be  sustained,  but  on 
the  frequency  of  its  application  and  the  range  of  variation  of 
its  amount.  The  structure  or  the  machine  must  usually  be 
designed  tcr  carry  indefinitely  whatever  load  it  is  intended  to 
sustain  and  to  be  permanently  safe,  however  much  the  stress 
may  vary,  or  however  frequent  its  application.  The  stress 
permitted  and  calculated  upon  must  therefore  be  less  as  the 
variation  is  greater,  and  as  the  frequency  of  its  application  is 
greater.  Although  it  is  customary  to  make  the  working  load 
one  fifth  or  one  sixth  the  maximum  load  that  could  be  sus- 
tained without  fracture,  it  has  now  become  well  known  that 
this  is  not  the  correct  method  except  for  an  unvarying  load  ; 
although,  as  will  be  seen,  these  factors  of  safety  are  sufficient 
to  cover  the  case  studied  by  Wohler. 

Wohler  found  that  good  wrought-iron  and  steel  would  bear 
loads  indefinitely  as  follows  : 


80  THE   STEAM-BOILER. 

Lbs.  per  sq.  in.  Kilogs  per  sq.  cm. 

Wrought-iron,  tension  only -f-  18,700  to  -f-         30;  -j-  1,309  to  -j-      2.2 

Wrought-iron,  tension  and  compres.  -|-    8.320  to  —     8,320;  -(-      582  to  —  582 

Cast-steel,  tension  only -j-  34.307  to  -j-  11,440;  -f-  2,401  to  -f-  801 

Cast-steel,  tension  and  compression  -j-  12,480  to  —  12,480;  -f-      874  to  —  874 

Thus  rupture  is  produced  either  by  a  certain  load,  called 
usually  the  "  breaking  load,"  once  applied,  or  by  a  repeatedly 
applied  smaller  load.  The  differences  of  stresses  applied,  as 
well  as  their  actual  amount,  determine  the  number  of  appli- 
cations which  may  be  made  before  fracture  occurs,  and  the 
length  of  life  of  the  member  or  the  structure.  This  weakening 
of  metal  by  repeated  stresses  is  known  as  fatigue.  It  is  not 
known  that  it  may  always  be  relieved,  like  internal  stresses,  by 
rest ;  but  it  is  apparently  capable  of  relief  frequently  by  either 
simple  rest  for  a  considerable  period,  or  by  heating,  working, 
and  annealing. 

The  experiments  described  seem  to  indicate  some  relation 
between  the  action  of  variable  loads  and  of  prolonged  stress 
where  metals  are  soft  enough  to  "  flow." 

Wohler  concluded  that  the  allowable  loads  for  the  cases  of 
stationary  loading,  loading  in  tension  alternating  with  entire 
relief,  and  equal  and  alternate  tensions  and  compressions,  will 
be  in  the  ratio  3:2:  I. 

The  method  above  described  is  still  in  the  experimental 
stage ;  but  it  may  be  provisionally  accepted  as  safer  than  the 
usual  method  of  covering  cases  of  varying  stresses  by  a  factor 
of  safety  determined  solely  by  custom  or  individual  judgment. 
It  has  been  the  custom  with  some  American  bridge-builders 
to  give  members  in  alternate  tension  and  compression  a  section 
equal  to  that  calculated  for  a  tension  under  static  load  equal 
to  the  sum  of  the  two  stresses — a  rough  method  of  meeting 
the  most  usual  and  serious  case. 

A  number  of  engineers,  commenting  upon  the  work  of 
Wohler,  Spangenberg,  Weyrauch,  and  Launhardt,  consider 
that  the  result  is  simply  to  base  upon  the  ultimate  strength  a 
deduced  limit  of  working  stress  which  corresponds  closely  to 
the  elastic  limit,  and  generally  urge  that  reasonable  factors  of 


MATERIALS— STRENGTH  OF    THE    STRUCTURE.  8l 

safety  related  to  the  limit  of  elasticity  are  preferable  to  the  still 
uncertain  method  above  described.  It  is  admitted,  however, 
that  the  results  accord  with  those  already  indicated  by  experi- 
ence where  a  definite  practice  has  become  settled  upon. 

There  are  many  phenomena  which  cannot  be  conveniently 
exhibited  by  strain-diagrams  ;  such  are  the  molecular  changes 
which  occupy  long  periods  of  time.  These  phenomena,  which 
consist  in  alterations  of  chemical  constitution  and  molecular 
changes  of  structure,  are  not  less  important  to  the  mechanic 
and  the  engineer  than  those  already  described.  Requiring 
usually  a  considerable  period  of  time  for  their  production,  they 
rarely  attract  attention,  and  it  is  only  when  the  metal  is  finally 
inspected,  after  accidental  or  intentionally  produced  fracture, 
that  these  effects  become  observable.  The  first  change  to  be 
referred  to  is  that  gradual  and  imperceptible  one  which,  occu- 
pying months  and  years,  and  under  the  ordinary  influence  of 
the  weather  going  on  slowly  but  surely,  results  finally  in  im- 
portant modification  of  the  proportions  of  the  chemical  ele- 
ments present,  and  in  a  consequent  equally  considerable 
change  of  the  mechanical  properties  of  the  metal. 

Exposure  to  the  weather,  while  producing  oxidation,  has 
another  important  effect :  It  sometimes  produces  an  actual  im- 
provement in  the  character  of  the  metal.  Old  tools,  which 
have  been  laid  aside  or  lost  for  a  long  time,  acquire  exceptional 
excellence  of  quality.  Razors  which  have  lost  their  keenness 
and  their  temper  recover  when  given  time  and  opportunity  to 
recuperate.  A  spring  regains  its  tension  when  allowed  to  rest. 
Farmers  leave  their  scythes  exposed  to  the  weather,  sometimes 
from  one  season  to  another,  and  find  their  quality  improved  by 
it.  Boiler-makers  frequently  search  old  boilers  carefully,  when 
reopened  for  repairs  after  a  long  period  of  service,  to  find  any 
tools  that  have  been  lost  and  so  improved. 

36.  A  Method  of  Detecting  any  Overstrain  to  which  a 
structure  or  either  of  its  parts  may  have  been  subjected,  which 
was  devised,  or  more  properly  discovered,  by  the  Author,  is 
sometimes  of  service  in  revealing  danger  of  accident,  or  the 
cause  of  disasters  already  arrived.  It  has  been  shown  by  the 
6 


82  THE   STEAM-BOILER. 

Author*  and  by  other  investigators,  that  when  a  metal  is  sub- 
jected to  stress  exceeding  that  required  to  strain  it  beyond  its 
original  apparent,  or  "  primitive,"  elastic  limit,  this  primitive 
elastic  limit  becomes  elevated,  and  that  strain-diagrams  obtained 
autographically,  or  by  carefully  plotting  the  results  of  well-con- 
ducted tests  of  such  metal,  are  "  the  loci  of  the  successive  limits 
of  elasticity  of  the  metal  at  the  successive  positions  of  set.""f 

It  has  been  shown  by  the  Author  also  that,  at  the  successive 
positions  of  set,  strain  being  intermitted,  a  new  elastic  limit  is, 
on  renewing  the  application  of  the  distorting  force,  found  to 
exist  at  a  point  which  approximately  measures  the  magnitude 
of  the  load  at  the  moment  of  intermission.^: 

Thus  it  is  seen  that  a  metal,  once  overstrained,  carries  per- 
manently unmistakable  evidence  of  the  fact,  and  can  be  made 
to  reveal  the  amount  of  such  overstrain  at  any  later  time  with 
a  fair  degree  of  accuracy.  This  evidence  cannot  be  entirely 
destroyed,  even  by  a  moderate  degree  of  annealing.  Often, 
only  annealing  from  a  high  heat,  or  reheating  and  reworking, 
can  remove  it  absolutely.  Thus,  too,  a  boiler,  or  any  structure, 
broken  down  by  causes  producing  overstrain  in  its  tension 
members,  or  in  its  transversely  loaded  beams  (and,  probably,  in 
compression  members — although  the  writer  is  not  yet  fully  as- 
sured of  the  latter),  retains  in  every  piece  a  register  of  the 
maximum  load  to  which  that  piece  has  ever  been  subjected  ; 
and  the  strain  sheet  of  the  structure,  as  strained  at  the  instant 
of  breaking  down,  can  be  thus  laid  down  with  a  fair  degree  of 
certainty.  The  Author  has  found  by  subsequent  tests  that 
transverse  strain  produces  the  same  effect  upon  the  elastic  limit 
for  tension. 

Here  may  be  found  a  means  of  tracing  the  overstrains 
which  have  resulted  in  the  destruction  or  the  injury  of  any 
iron  or  steel  structure,  and  of  ascertaining  the  cause  and  the 
method  of  its  failure,  in  cases  frequently  happening  in  which 

*  See  Trans.  Am.  Soc.  C.  E.,  1874  et  seq.,  Journal  Franklin  Institute,  1874  ; 
Van  Nostrand's  Eclectic  Engineering  Magazine,  1874,  etc.,  etc. 

f  On  the  Strength,  etc..  of  Materials  of  Construction,  1874,  Sec.  20. 

\  On  the  Mechanical  Treatment  of  Metals;  Metallurgical  Review,  1877; 
Engineering  and  Mining  Journal,  1877. 


MATERIALS— STRENGTH  OF   THE    STRUCTURE.  83 

they  are  indeterminable  by  any  of  the  usual  methods  of  inves- 
tigation. 

This  method  may  thus  sometimes  be  used  to  ascertain  the 
probable  cause  of  a  boiler  explosion,  by  determining  whether 
the  metal  has  been  subjected  to  overstrain  in  consequence  of 
overpressure.  The  causes  of  accidents  to  machinery  may  also 
be  thus  detected,  and  many  other  applications  might  be  sug- 
gested. 

37.  The  Effect  of  Temperature  and  its  Variation  on  iron 
and  steel  is  probably  the  most  important  of  all  those  phenom- 
ena which  modify  the  behavior  of  iron  or  steel  under  load. 


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32  03              100              2O             3    O              4-OO              50O             6OO             700              800             900             1000          1100  G. 
82°              212             392            572.           752             932            1112            1292            1472           1652            1832      F. 

FIG.  53.— HEAT  vs.  TENACITY. 

The  diagram  above*  graphically  represents  the  results  of 
several  series  of  experiments. 

Curves  Nos.  i  and  2  represent  Kollmann's  experiments  on 
iron,  and  3  on  Bessemer  "steel."  No.  I  is  ordinary,  and  2 
steely  puddled  iron. 

Curve  No.  4  represents  the  work  of  the  Franklin  Institute 
on  wrought-iron. 


*  Eisen  und   Stahl,  A.    Martens  ;  Zeitschritt  des  Vereins  Deutscher  Inge- 
nieure  ;  Feb.  1883,  p.  127. 


84  THE   STEAM-BOILER. 

Curve  No.  5  gives  Fairbairn's  results,  working  on  English 
wrought-irons. 

Nos.  6  to  II  are  Styffe's,  and  represent  the  experiments 
made  by  him  on  Swedish  iron.  The  numbers  do  not  appear, 
as  these  results  do  not  fall  into  curves ;  these  results  are  indi- 
cated by  circles,  each  group  being  identified  by  the  peculiar 
filling  of  the  circles,  as  one  set  by  a  line  crossing  the  centre, 
another  by  one  across,  a  third  by  a  full  circle,  etc. 

The  broken  lines,  12  and  13,  are  British  Admiralty  experi- 
ments on  blacksmiths'  irons,  and  No.  14  on  Siemens  steel. 

The  first  five  series  only  are  of  value  as  indicating  any  law ; 
and  they  exhibit  plainly  the  general  tendency  already  referred 
to,  to  a  decrease  of  tenacity  with  increase  of  temperature. 

Fairbairn's  experiments,  No.  5,  best  exhibit  the  maximum, 
first  noted  by  the  Committee  of  the  Franklin  Institute,  at  a 
temperature  between  that  of  boiling  water  and  the  red  heat. 

It  will  be  observed  that  the  measure  of  tenacity,  at  the  left,. 
is  obtained  by  making  the  maximum  of  Kollmann  unity.  It 
will  also  be  noted  that  Kollmann  does  not  find  a  maximum  as 
in  curves  4  and  5,  but,  on  the  contrary,  a  more  rapid  reduction 
in  strength  at  that  temperature  than  beyond. 

It  would  seem,  therefore,  that  that  peculiar  phenomenon 
must  be  due  to  some  accidental  quality  of  the  iron.*  The 
Author  has  attributed  it  to  the  existence  in  the  iron,  before 
test,  of  internal  stresses  which  were  relieved  by  flow  as  the 
metal  was  heated,  disappearing  at  a  temperature  of  300°  or 
400°  Fahr.  (149°  to  204°  Cent.). 

The  experiments  of  Mr.  Oliver  Williams  f  in  determining 
the  change  produced  in  the  character  of  the  fracture  of  iron  by 
transverse  strain,  at  extreme  temperatures,  indicate  loss  of  duc- 
tility at  low  temperatures. 

Two  specimens  of  nut-iron,  from  different  bars,  made  at 
Catasauqua,  Pennsylvania,  were  first  nicked  with  a  cleft  on  one 
side  only,  and  then  broken  under  a  hammer,  at  a  temperature 


*  Isherwood  suggests  that  this  is  simply  due  to  repeatedly  breaking  the  same 
piece. 

f  The  Iron  Age,  New  York,  March  13,  1873,  p.  16. 


MATERIALS— STRENGTH  OF    THE   STRUCTURE.  85 

of  about  20°  Fahr.  (—  f  Cent.).  At  this  temperature  both 
specimens  broke  off  short,  showing  a  clearly  defined  granular 
or  steely  iron  fracture.  The  pieces  were  then  gradually  heated 
to  about  75°  Fahr.  (24°  Cent.),  and  then  broken  as  before,  de- 
veloping a  fine,  clear,  fibrous  grain.  The  two  fractures  were 


FIG.  54. — FRACTURE  AT  ORDINARY  TEMPERATURE. 

but  four  inches  (10.16  centimetres)  apart,  and  are  entirely  dif- 
ferent. The  accompanying  illustrations,  from  the  Author's 
collection,  exhibit  this  case. 

It  has  been  long  known  that  a  granular  fracture  may  be 
produced  by  a  shock,  in  iron  which  appears  fibrous  when  grad- 
ually torn  apart.  This  was  fully  proven  by  Kirkaldy.*  Mr. 
Williams  was,  probably,  the  first  to  make 
the  experiment  just  described,  and  thus 
to  make  a  direct  comparison  of  the  char- 
acteristics of  fracture  in  the  same  iron  at 
different  temperatures. 

Valton  has  found  f  that  some  iron  be- 
comes brittle  at  temperatures  of  572°  or 
752°  Fahr.  (300°  to  400°  Cent.),  and  re- 
gains ductility  and  toughness  at  higher 
temperatures.  On  the  whole,  the  frac-  "  55T  ] 

*  Experiments  on  Iron  and  Steel. 

f  Bulletin  Iron  and  Steel  Assoc.,  Feb.  1877. 


86  THE    STEAM-BOILER. 

ture  of  iron  at  low  temperatures  has  been  found  to  be  charac- 
teristic of  a  brittle  material,  while  at  higher  temperatures  it 
exhibits  the  appearance  peculiar  to  ductile  and  somewhat  vis- 
cous substances.  The  metal  breaks,  in  the  first  case,  with  slight 
permanent  set  and  a  short  granular  fracture,  and  in  the  latter 
with,  frequently,  a  considerable  set,  and  the  form  of  fracture  in- 
dicating great  ductility.  The  variation  in  the  behavior  of  iron, 
as  it  approaches  the  welding  heat,  illustrates  the  latter  condi- 
tion in  the  most  complete  manner. 

Valton  found  that  a  steel  rod  bent  very  well  at  a  tempera- 
ture a  little  below  dull  red,  but  broke  at  a  temperature  which 
may  be  called  blue,  the  fracture  showing  that  color.  Portions 
of  the  rod  which  were  below  this  temperature  manifested  much 
toughness,  and  bent  without  fracture.  Charcoal  pig-iron  from 
Tagilsk,  made  in  1770,  irons  obtained  from  the  Ural  in  rods 
and  sheets,  soft  Bessemer  and  Martin  steels  from  Terrenoire, 
soft  English  steel  and  good  English  merchant-bars,  all  gave 
the  same  results,  whether  the  metal  tested  had  been  hammered 
or  rolled.  Valton  found  that  the  phenomenon  had  been  long 
known  to  the  workmen  under  his  direction.  In  working  sheet- 
iron  with  the  hammer  they  wait  until  the  metal  has  cooled 
further  when  approaching  the  temperature  which  would  give 
the  blue  fracture  when  broken.  He  concludes  that  wrought- 
irons,  as  well  as  some  kinds  of  soft  steel,  even  when  of  excel- 
lent quality,  are  very  brittle  at  a  temperature  a  little  below 
dull  red  heat — 577°  to  752°  Fahr.  (between  300°  and  400°  Cent.). 

The  variation  of  strength  follows  quite  closely  the  change 
of  density,  which  latter  is  illustrated  in  the  preceding  diagram,, 
which  exhibits  increase  of  volume  from  the  freezing-point. 

The  sudden  fall  of  the  line  before  reaching  the  melting- 
point  indicates  the  sudden  increase  of  volume  which  castings 
exhibit  while  cooling,  and  which  enables  "sharp"  castings  to 
be  secured.  It  is  at  the  crest  noted  near  this  point  that  vis- 
cosity is  observed.  From  this  point  back  to  the  freezing-point 
the  variation  follows  a  regular  law. 

It  would  thus  seem  that  the  general  effect  of  increase  or 
decrease  of  temperature  is,  with  solid  bodies,  to  decrease  or 
increase  their  power  of  resistance  to  rupture,  or  to  change  of 


MA  TERIALS—  STRENGTH  OF   THE   STRUCTURE.  8/ 

form,  and  their  capability  of  sustaining  "dead"  loads;  and  we 
may  conclude : 

(1)  That  the  general  effect  of  change  of  temperature  is  to 
produce  change  of  ductility,  and  consequently  change  of  resili- 
ence, or  power  of  resisting  shocks  and  of  carrying  "  live  loads." 
This  change  is  usually  opposite  in  direction  and  greater  in  de- 
gree   at    ordinary  temperatures  than  the  variation  simultane- 
ously occurring  in  tenacity. 

(2)  That  marked  exceptions  to  this  general  law  have  been 
noted,  but  that  it  seems  invariably  the  fact  that,  wherever  an 
exception  is  observed  in  the  influence  upon  tenacity,  an  excep- 
tion may  also  be  detected  in  the  effect  upon  resilience.     Causes 
which  produce  increase  of  strength  seem  also  to  produce  a  sim- 
ultaneous decrease  of  ductility,  and  vice  versa. 

(3)  That  experiments  upon  copper,  so  far  as  they  have  been 
carried,  indicate  that   (as  to  tenacity)   the    general  law  holds 
good  with  that  metal. 

(4)  That  iron  exhibits  marked  deviations  from  the  law  be- 
tween ordinary  temperatures  and  a  point  somewhere  between 
500°  and  600°  Fahr.  (260°  and  316°  Cent.),  the  strength  increas- 
ing between  these  limits  to  the  extent  of  about  15  per  cent 
with  good  iron.     The  variation  becomes  more  marked  and  the 
results  more  irregular  as  the  metal  is  more  impure. 

(5)  That  above  600°  Fahr.  (316°  Cent.)  and  below  70°  (21° 
Cent.)  the  general  law  holds  good  for  iron,  its  tenacity  increas- 
ing with  diminishing  temperature  below  the  latter  point  at  the 
rate  of  from  0.02  to  0.03  per  cent  for  each  degree  Fahrenheit, 
while  its  resilience  decreases  in  an  undetermined  ratio  for  good 
iron,  and  to  the  extent  of  reduction  to  one  third  its  ordinary 
value  or  less,  at   10°  Fahr.  ( —  12°  Cent.)  when  cold-short,  and 
in   the   latter  case  the  set   may  be  less  than  one  fourth  that 
noted  at  a  temperature  of  84°  Fahr.  (29°  Cent.). 

(6)  That  the  viscosity,  ductility,  and  resilience  of  metals  are 
determined  by  identical  conditions,   and  that  the   fracture  of 
iron   at   low  temperatures  has  accordingly  been  found  to   be 
characteristic  of  a  brittle  material,  while  at  the  higher  tempera- 
tures it  exhibits  the  appearance  peculiar  to  ductile  and  some- 
what viscous  substances.     The  metal  breaks  in  the  first  case 


88  THE    STEAM-BOILER. 

with  slight  permanent  set  and  a  short  granular  fracture,  and  in 
the  latter  with  frequently  a  considerable  set  and  a  form  of  frac- 
ture indicating  great  ductility.  The  variation  in  the  behavior 
of  iron,  as  it  approaches  a  welding  heat,  illustrates  the  latter 
condition  in  the  most  complete  manner. 

(7)  That  the  precise  action  of  the  elements  with  which  iron 
is  liable  to  be  contaminated,  and  the  extent  to  which  they 
modify  its  behavior  under  varying  temperature,  remain  to  be 
fully  investigated,  but  that  the  presence  of  phosphorus  and  of 
other  substances  producing  "  cold-shortness,"  exaggerates  to  a 
great  degree  the  effects  of  low  temperature  in  producing  loss 
of  toughness  and  resilience. 

(8)  That   the   modifications  of  the  general  law  with   other 
metals  than  iron  and  copper,  and  in  the  case  of  alloys,  have 
not  been  studied,  and  are  entirely  unknown. 

The  practical  result  of  the  whole  investigation  is  that  iron 
and  steel,  and  probably  other  metals,  do  not  lose  their  power 
of  sustaining  absolutely  "  dead  "  loads  at  low  temperatures,  but 
that  they  do  lose,  to  a  very  serious  extent,  their  power  of  sus- 
taining shocks  or  of  resisting  sharp  blows,  and  that  the  factors 
of  safety  in  structures  need  not  be  increased  in  the  former 
case,  where  exposure  to  severe  cold  is  apprehended  ;  but  that 
machinery,  rails,  and  other  constructions  which  are  to  resist 
shocks  should  have  larger  factors  of  safety,  and  should  be  most 
carefully  protected,  if  possible,  from  extreme  temperatures. 

The  Stress  Produced  by  Change  of  Temperature  is  easily  cal- 
culated when  the  modulus  of  elasticity  and  the  coefficient  of 
expansion  are  known,  thus : 

Let  E  =  the  modulus  of  elasticity; 

A  =  the  change  of  length  per  degree  and  per  unit  of 

length  ; 

Af  =  the  difference  of  initial  and  final  temperatures ; 
/  =  the  stress  produced. 

Then 

p\E\\  A J/°  :  I, 

.-./  =  \EAf (i) 


MATERIALS— STRENGTH  OF    THE   STRUCTURE.  89 

For  good  wrought-iron  and  steel,  taking  E  as  28,000,000 
pounds  on  the  square  inch,  or  2,000,000  kilogrammes  on  the 
square  centimetre,  and  A  as  0.0000068  for  Fahrenheit,  and  as 
O.OOOOI2O  for  Centigrade  degrees: 

Fahr.,  nearly,  ) 

\ (2) 

Cent.,  nearly.  ) 

For  cast-iron,  taking  E  =  16,000,000;  A  =  0.0000062: 

/  =  ioo///°  Fahr.,  nearly,  ) 

(3) 

=     \2dt°  Cent.,  nearly.  ) 

This  force  must  be  allowed  for  as  if  a  part  of  the  tension, 
T,  or  compression,  C,  produced  by  the  working  load  when  the 
parts  are  not  free  to  expand. 

Sudden  Variation  of  Temperature  has  an  effect  upon  steel 
which  is  very  great  when  the  proportion  of  carbon  is  not  far 
from  one  per  cent.  With  less  carbon  the  effect  is  less  observ- 
able, and  with  the  wrought-irons  and  with  ingot  metals  con- 
taining less  than  one  third  per  cent  carbon  and  other  hardening 
elements,  it  becomes  quite  unimportant.  Soft  irons  are  still 
further  softened  by  sudden  reduction  of  temperature  from  the 
red  heat.  Cast-irons,  unless  of  the  class  known  as  "  chilling 
irons,"  are  much  less  affected  than  steel,  and  when  very  rich  in 
graphitic  carbon  are  not  perceptibly  hardened. 

When  either  iron  or  steel  is  repeatedly  heated  and  cooled, 
a  permanent  change  of  form  takes  place.  Colonel  Clarke  has 
shewn*  that  cylinders  repeatedly  heated  to  a  high  temperature 
and  suddenly  cooled,  become  enlarged  in  diameter  perma- 
nently. Pieces  of  tempered  steel  are  larger  than  when  untem- 
pered. 

Cast-iron  ordnance,  after  having  been  discharged  many 
times,  becomes  unsafe  in  consequence  of  weakening,  which  is 


*  Philosophical  Magazine,  1863. 


90  THE   STEAM-BOILER. 

probably  principally  due  to  strains  caused  by  sudden  and  irreg- 
ular changes  of  temperature  in  service. 

Such  grades  of  steel  as  take  a  temper  are  greatly  strength- 
ened unless  too  highly  hardened,  in  which  case  they  become 
brittle  from  internal  stresses.  The  Author  has  found  temper- 
ing in  mercury  to  increase  greatly  both  the  strength  and  the 
toughness  of  small  pieces  of  good  tool  steel.  Kirkaldy  has 
found,  by  an  extended  series  of  experiments,  that  tempering 
tool  steels  in  oil  greatly  increases  both  strength  and  elasticity, 
while  hardening  in  water  reduces  both.  The  higher  the  tem- 
perature at  which,  without  risk,  the  steel  can  be  cooled,  the 
greater  is  this  increase  of  strength.  Hard  steels  exhibit  the 
fact  better  than  soft  steels.  Dividing  steels  into  series  in  the 
order  of  their  contents  in  carbon,  beginning  with  the  softest 
grades,  the  following  were  the  percentages  of  increase  of 
strength  from  weakest  to  strongest:  u.8,  24.2,  40.7,  53.2,  57.0, 
64.1,  70.9,  77.6.  The  harder  steels  were  highly  heated;  the 
soft  steels  only  moderately. 

A  singular  change  is  observed  in  iron  and  in  the  soft  steelsy 
and  may  perhaps  be  found  to  occur  with  other  metals,  when 
the  temperature  approaches  what  is  known  as  the  black  heat — a 
temperature  not  far  from  600°  or  700°  F.  (316°  to  370°  C),  and 
below  a  red-heat  visible  in  the  dark.  At  this  temperature, 
metal  which  bends  readily  either  cold  or  at  the  full  red  heat 
is  found  to  be  exceedingly  brittle  and  to  break  easily,  especially 
under  percussion,  without  bending.  This  heat  with  its  peculiar 
effect  may  be  reached  in  a  bath  of  boiling  tallow  at  a  little 
above  the  lower  temperature  above  specified.  The  steels  show 
less  of  this  effect,  usually,  than  the  irons.  The  presence  of 
more  than  a  trace  of  sulphur,  or  phosphorus,  or  of  other 
hardening  elements,  exaggerates  this  action. 

38.  Crystallization  and  Granulation  are  the  two  methods 
of  alteration  of  molecular  structure  which  are  consequent  upon 
the  action  of  any  cause  which  continually  separates  the  par- 
ticles of  the  metal  beyond  the  range  marked  and  limited  by 
the  elastic  limit.  No  evidence  is  to  be  found  that  a  single 
suddenly  applied  force,  producing  fracture,  may  cause  such  a 
systematic  and  complete  rearrangement  of  molecules.  The 


MATERIALS— STRENGTH  OF    THE    STRUCTURE.  9! 

granular  fracture  produced  by  sudden  breaking,  and  the  crys- 
talline structure  produced  as  above  during  long  periods  of  time, 
are  apparently  as  distinct  in  nature  as  they  are  in  their  causes. 
But  simple  tremor,  where  no  sets  of  particles  are  separated  so 
far  as  to  exceed  tJie  elastic  range,  and  to  pass  beyond  the  limit 
of  elasticity,  does  not  seem  to  produce  such  changes.  In  fact, 
some  of  the  most  striking  illustrations  of  the  improvement  in 
the  quality  of  wrought-iron  with  time  have  occurred  where 
severe  jarring  and  tremor  were  common.  Metal  has  been  sub- 
jected for  many  years  to  the  strains  and  tremor  accompanying 
the  passage  of  trains  without  apparent  tendency  to  crystalliza- 
tion, and  with  evident  improvement  in  its  quality. 

Wohler  found  cubic  crystals  in  cast-iron  plates  which  had 
been  for  some  time  kept  at  nearly  the  temperature  of  fusion  in 
a  furnace,  and  Augustine  found  similar  crystals  in  gun-barrels; 
Percy  found  octahedra  of  considerable  size  in  a  bar  which  had 
been  used  in  the  melting-pot  of  a  glass-furnace.  Fairbairn  as- 
serts the  occasional  occurrence  of  such  change  due  to  shock, 
jar,  and  long-continued  vibration.  Miller  found  cubic  crystal- 
lization plainly  exhibited  in  Bessemer  iron,  which  may,  how- 
ever, have  been  due  to  the  presence  of  manganese.  Hill 
shows  *  that  heat  may  produce  such  crystallization. 

In  a  discussion  which  took  place  many  years  ago  before  the 
British  Institution  of  Civil  Engineers,  Mr.  J.  E.  McConnell 
produced  a  specimen  of  an  axle  which  he  thought  furnished 
nearly  incontestable  evidence  of  crystallization.  One  portion 
of  this  axle  was  clearly  of  fibrous  iron,  but  the  other  end  broke 
off  as  short  as  glass.  The  axle  was  hammered  under  a  steam 
hammer,  then  heated  again  and  allowed  to  cool,  after  which  it 
was  found  necessary  to  cut  it  almost  half  through  and  hammer 
it  for  a  long  time  before  it  could  be  broken.  The  great  testing- 
machine  at  the  Washington  Navy  Yard  has  a  capacity  of  about 
300  tons,  and  has  been  in  use  40  years.  Commander  Beardslee 
subjected  it  to  a  stress  of  288,000  Ibs.  (130,000  kilogrammes), 
which  stress  had  frequently  been  approached  before ;  but  it 
subsequently  broke  down  under  about  100  tons.  The  connect- 

*  Iron  Age,  1882  ,  Mechanics,  1882. 


92 


THE   STEAM-BOILER. 


ing-bar  which  gave  way  had  a  diameter  of  five  inches,  and 
should  have  originally  had  a  strength  of  about  400  tons  (406,400 
kilogrammes).  Examining  it  after  rupture,  the  fractured  sec- 
tion was  found  to  exhibit  strata  of  varying  thickness,  each 
having  a  characteristic  form  of  break.  Some  were  quite  granu- 
lar in  appearance,  but  the  larger  proportion  were  distinctly 
crystalline.  Some  of  these  crystals  are  large  and  well  defined. 
The  laminae,  or  strata,  preserve  their  characteristic  peculiarities, 
whether  of  granulation  or  of  crystallization,  lying  parallel  to 
their  axis  and  extending  from  the  point  of  original  fracture  to 
a  section  about  a  foot  distant,  where  the  bar  was  broken  a 
second  time  (and  purposely)  under  a  steam  hammer.  It  thus 
differs  from  the  granular  structure  which  distinguishes  the  sur- 
faces of  a  fracture  suddenly  produced  by  a  single  shock,  and 
which  is  so  generally  confounded  with  real  crystallizion. 

39.  Irons  and  Steels  Compared  with  reference  to  their 
composition  and  qualities,  even  when  the  latter  are  given  as 
much  of  the  character  of  the  best  iron  as  is  possible,  will  ex- 
hibit some  marked  differences. 

In  composition  the  following  maybe  considered  good  repre- 
sentative examples: 


IRONS. 

STE 

ELS. 

Swedish. 

Dartmoor. 

Pennsylva- 
nia. 

"Mild." 

Very 

"Mild." 

Carbon 

O  087 

o  016 

o  067 

o  238 

O   OOQ 

Silicon       .      

o  056 

o  022 

O  O2O 

o  10^ 

o  163 

Sulphur     

o  ooc 

o  104 

O  OOI 

O   OI2 

O   OOQ 

Phosphorus  

o.  1  06 

O.O75 

O.O'M 

w.  wwy 

o  084 

Manganese 

o  280 

O   OOQ 

o  184 

o  620 

Iron  by  cliff      .         . 

QQ    22O 

QQ    ^72 

QQ    828 

QQ   4.27 

QQ    11^ 

IOO.OOO 

IOO.OOO 

IOO.OOO 

IOO.OOO 

IOO.OOO 

All  the  hardening  elements  usually  appear  in  larger  propor- 
tion in  the  steels  than  in  the  irons;  but  this  is  not  invariably 
the  fact,  especially  with  those  very  mild  steels  which  can  be 
made  by  the  crucible  process. 

Comparing  the  analyses  of  the  two  classes  of  metal,  it  will 
be  found  that  the  best  irons  are  more  irregular  and  uncertain 


MATERIALS—  STRENGTH   OF    THE   STRUCTURE.  93 

in  composition  than  the  best  steels;  that  they  contain  con- 
siderable amounts  of  cinder,  or  slag,  derived  from  the  puddle- 
ball  and  the  crude  cast-iron  from  which  it  is  made ;  that  the 
carbon  and  silicon  are  usually  less  in  quantity,  though  very 
variable ;  sulphur  and  phosphorus  are  commonly  "  higher"  than 
in  steels;  and  the  whole  list  of  elements,  aggregating,  slag 
aside,  less  in  the  irons  than  in  the  steels,  varies  greatly  in  pro- 
portions, and  by  no  law.  The  steels  are  capable  of  more  exact 
prescription  of  constitution  than  irons,  and  are  especially  dis- 
tinguished by  their  richness  in  manganese,  silicon,  and  carbon, 
and  their  freedom  from  slag  and  from  sulphur  and  phosphorus. 
The  crucible  steels  contain,  as  a  rule,  much  less  manganese  and 
silicon  than  do  the  others.  For  boiler-plate,  the  carbon  should 
be  kept  below  one  fourth  of  one  per  cent,  and  all  other  ele- 
ments as  low  as  possible ;  but  the  effect  of  manganese  and 
other  hardening  constituents  is  not  sufficiently  well  settled, 
especially  where  the  metal  is  exposed  to  the  action  of  the  fire, 
and  to  varying  temperatures  generally,  to  admit  of  the  pre- 
scription of  a  formula  for  the  best  possible  composition. 

Comparing  the  structure  of  iron  and  steel,  it  will  be  found 
that  the  latter  is  comparatively,  often  almost  absolutely,  homo- 
geneous ;  while  the  former  is  very  irregularly  laminated,  and 
exhibits  the  most  remarkable  fibrous  texture  when  broken 
slowly,  the  slag  separating  threads  of  metal  by  encasing  them 
in  sheaths  of  mineral,  and  layers  of  cinder  and  oxide  causing 
stratification  by  preventing  the  welding  of  the  sheets  of  thinner 
iron  of  which  the  plate  is  made.  The  whole  structure  of  the 
"  pile"  from  which  it  is  rolled  is  reproduced  in  a  distorted 
fashion  in  the  finished  plates.  The  steel  breaks  with  the  same 
fracture,  and  offers  the  same  resistance  in  both  directions; 
while  iron,  especially  the  cheaper  grades,  usually  resists  longi- 
tudinal forces  much  better  than  transverse. 

In  tenacity  the  best  steel  boiler-plate  is  but  little,  if  any, 
stronger  than  the  best  boiler-iron  :  it  excels  the  latter,  however, 
in  ductility  as  well  as  in  homogeneousness,  and  resists  the  cor- 
roding action  of  the  fluids  with  which  it  is  brought  in  contact 
much  better  than  iron.  If  too  rich  in  manganese,  too  high  in 
carbon  or  silicon,  or  if  it  contains  an  appreciable  amount  of 


94  THE   STEAM-BOILER. 

phosphorus,  steel  becomes  unreliable,  and  more  dangerous  than 
ordinary  irons. 

" Mild Steel"  will  take  a  temper,  often,  when  containing  over 
0.30  per  cent  of  carbon.  Its  uniformity  and  reliability  decrease 
as  its  strength  and  hardness  increase,  and  also  with  increase  of 
thickness  and  size  of  the  mass  produced.  This  fact  has  caused 
the  British  Lloyds  regulations  to  make  the  following  allowances : 

Plates  and  stays  o  to  I  inch  thick,  maximum  tensile  strength 
67,200  pounds  (4724  kgs.  per  sq.  cm.). 

Plates  and  stays  I  to  if  inches  thick,  maximum  tensile 
strength  64,960  pounds  (4567  kgs.  per  sq.  cm.). 

Plates  and  stays  over  i-f  inches  thick,  maximum  tensile 
strength  62,720  pounds  (4410  kgs.  per  sq.  cm.). 

The  same  proportions  carried  further  would  reduce  the  al- 
lowable tenacity  of  steel  in  heavy  and  thick  masses  to  that  of 
good  iron,  leaving  its  homogeneousness  the  only  advantage. 

If  used  at  all,  the  harder  steels  should  be  tempered  in  oil  ; 
but  they  have  no  place  in  boiler-construction. 

The  conclusions  to  be  to-day  reached  after  comparing  steel 
and  iron  as  materials  for  boiler-construction,  and  in  view  of  ex- 
perience to  date  in  their  use,  are  fully  confirmatory  of  the  as- 
sertion of  the  late  Mr.  A.  L.  Holley,  written  a  generation  ago  :* 
"  It  appears  extremely  probable  that  this  material  "  (steel)  "  will 
gradually  come  into  exclusive  service,  not  only  increasing  the 
safety  and  decreasing  the  repair  expense  of  boilers,  but  pro- 
moting the  economy  of  steam  generation  and  of  railway  work- 
ing generally." 

40.  The  Characteristics  of  Iron  Plate  used  in  boiler- 
making  must  all  be  in  accordance  with  the  requirements  already 
stated.  A  number  of  different  qualities  of  both  iron  and  steel 
are  sent  into  the  market  for  use  in  boiler-construction.  Of 
these  the  makes  and  qualities  of  iron  have  been  long  well 
settled  ;  but  the  best  qualities  and  compositions  of  steel  are 
not  as  well  established.  No  hard  steels,  however,  are  classed 
as  boiler-steels. 

Good  Boiler-plate   is   commonly  assumed    to   be   made    of 

*  American  and  European  R  ilway  Practice,  p.  29. 


MATERIALS— STRENGTH   OF    THE    STRUCTURE.  95 

"  charcoal  iron,"  i.e.,  of  iron  made  from  pig-iron  produced  in 
the  charcoal  blast-furnace,  no  other  fuel  than  wood-charcoal 
being  used.  The  scarcity  of  charcoal  and  the  cost  of  such  irons 
is  gradually  making  it  more  and  more  difficult  to  secure  them. 
American  boiler-plate  is  classed  by  the  following-named 
brands : 

"  Charcoal  No.  I  iron"  (C.  No.  i)  is  made  entirely  of  char- 
coal iron  ;  it  has  a  tenacity  exceeding  40,000  pounds  per  square 
inch  (2812  kgs.  per  sq.  cm.),  is  hard,  but  not  very  ductile,  and 
is  never  used  when  flanging  or  considerable  change  of  form  is 
required,  as  it  is  apt  to  break  at  the  bend.  When  reheated  and 
reworked  to  form  what  is  called  "  charcoal  No.  I  reheated 
iron"  (C.  No.  I,  R.  H.)  it  becomes  still  harder,  and  is  found  to 
wear  well  in  fireboxes,  but  is  still  less  well  fitted  than  before 
for  flanging  and  working,  on  account  of  its  increased  brittleness. 

"  Charcoal  Hammered  No.  I  Shell-iron"  (C.  H.  No.  i,  S.)  is 
a  better  worked  iron  than  C.  No.  i ;  but  it  is  not  always  ham- 
mered. It  is  stronger,  having  a  tenacity  of  50,000  to  55,000 
pounds  per  square  inch  (3515  kgs.  per  sq.  cm.  to  3838)  in  the 
direction  of  the  fibre,  and  seventy-five  or  eighty  per  cent  of 
this  amount  across  the  grain.  This  grade  is  not  usually 
flanged,  but  may  be  bent  if  handled  with  care,  and  if  the 
radius  of  curvature  is  made  sufficiently  great ;  it  is  sold  princi- 
pally for  use  in  the  shells  of  boilers.  A  better  quality  known 
as  "flange-iron"  (C.  H.  No.  i,  F.)  is  much  more  ductile,  and 
may  be  worked  into  flanged  sheets ;  it  is  nearly  equally  strong 
in  both  directions,  and  has  about  the  tenacity  of  the  preceding. 
A  still  harder  grade  of  hammered  iron  is  intended  for  fireboxes 
mainly  (C.  H.  No.  i,F.  B.),  and  especially  for  flue-sheets,  which 
are  flanged  to  receive  the  flues;  and  a  still  better  grade  (C.  H. 
No.  i,  F.  F.  B.)  called  "  charcoal  hammered  No.  i,  flange  fire- 
box" iron,  extra  firebox,  or,  sometimes,  best  firebox,  is  made, 
which  is  more  generally  considered  best  for  this  use. 

All  the  grades  of  charcoal-irons  have  been  made  principally 
in  Pennsylvania. 

"  Shell "  boiler-plate  has  often,  if  not  generally,  an  outer 
skin  of  charcoal-iron,  the  "  pile"  from  which  it  is  rolled  being 
composed  of  other  irons,  and  covered  top  and  bottom  with 


^  THE   STEAM-BOILER. 

pieces  of  charcoal-iron.  Although  distinctively  made  for  the 
shell  of  the  boiler,  the  best  makers  usually  prefer  to  use  better 
grades  for  that  purpose. 

"Refined"  Iron  is  used  for  miscellaneous  purposes  when 
strength  and  toughness  are  not  specially  demanded,  and  where 
no  risks  are  involved.  It  is  not  intended  for  boiler-making; 
it  is  made  directly  from  the  pig-iron.  "  Tank"  iron  is  a  still 
cheaper  grade,  used  only  for  the  most  unimportant  purposes. 
Neither  of  these  grades  should  be  used  in  boilers,  or  in  any 
structure  of  great  magnitude  or  value. 

The  best  British  boiler  and  smith's  irons  are  made  in  York- 
shire, the  best  known  in  the  United  States  being  those  from 
the  Low  Moor,  the  Bowling,  and  th*e  Farnley  works,  and  sold 
in  the  trade  as  "  best  Yorkshire"  irons. 

41.  The  Manufacture  of  Boiler-plate,  iron  or  steel,  is  not 
essentially  different  in  method  from  the  making  of  other  iron 
and  steel  "  uses."  Iron  boiler-plate  is  made  from  puddled  or 
scrap  iron,  the  process  of  puddling  being  always  that  which  is 
resorted  to  in  the  reduction  of  the  carbon  and  the  production 
of  the  wrought-iron  from  the  cast.  In  the  rolling  of  plates,  the 
wrought-iron,  in  bars,  slabs,  or  miscellaneous  scrap,  is  formed 
into  "  piles"  of  the  proper  size  and  form,  which,  after  being 
heated  to  a  full  welding  temperature,  are  passed  through  a 
heavy  roll-train  of  sufficient  size  and  power  to  weld  the  con- 
stituent pieces  into  a  comparatively  solid  mass,  and  to  reduce 
that  mass  to  the  desired  thickness.  The  pile  is  made  of  such 
size  and  shape  as  may  be  found  to  give  the  proper  form  and 
dimensions  of  sheet. 

Steel  plate  is  oftenest  produced  by  the  Siemens-Martin 
process  of  reduction  of  cast  with  wrought  iron  of  selected  qual- 
ities, in  the  "  open-hearth"  or  Siemens  regenerative  furnace, 
securing  freedom  from  cinder  by  stirring,  and  from  oxide  by 
the  addition  of  manganese  in  the  form  either  of  spiegeleisen 
for  hard  or  of  ferro-manganese  for  soft  steels,  and  then,  while 
still  very  fluid,  tapping  into  the  ingot-mould,  whence  the  ingot, 
when  sufficiently  cooled,  is  taken  to  be  rolled  into  plate.  An 
intermediate  reheating  of  the  ingot,  or  a  period  of  "  soaking"  in 
hot  "  soaking-pits,"  is  very  generally  found  advisable  to  secure 


MATERIALS— STRENGTH  OF    THE    STRUCTURE.  97 

a  comparative  uniformity  of  temperature  throughout  the  ingot, 
in  order  that  it  may  be  successfully  rolled. 

The  Bessemer  process  produces  "steel,"  or  more  correctly 
u  ingot-iron,"  boiler-plate  by  a  very  similar  series  of  chemical 
operations;  but  it  usually  deals  with  larger  masses,  and  fur- 
nishes, as  a  rule,  harder  steels.  The  rolling  of  steel  demands 
the  use  of  more  powerful  roll-trains  than  are  needed  in  rolling 
iron. 

Comparing  the  two  processes,  it  is  seen  that  the  wrought- 
iron  plate  must  necessarily  retain  some  of  the  slag  which  came 
into  it  from  the  puddle-ball,  and  that  it  must  be  liable  to  de- 
fects in  welding  where  the  several  pieces  of  which  the  pile  is 
composed  come  together,  especially  should  those  surfaces  be 
covered,  as  is  often  the  case,  with  a  heavy  coating  of  oxide. 
Iron  plate  must  thus  always  exhibit  some  defect  of  homo- 
geneousness,  and  may  be  seriously  defective  in  consequence  of 
"  lamination"  produced  as  just  described.  On  the  other  hand, 
steel,  whether  made  by  the  crucible,  the  Bessemer,  or  the 
Siemens-Martin  process,  is  always  very  uniform  in  texture,  and 
is  usually  so  in  composition.  The  molten  mass  allows  all  slag 
and  oxide  to  rise  to  its  surface,  and  thus  the  fibrous  and  lami- 
nar character  of  iron  is  avoided,  while  the  subsequent  processes 
do  not  involve  necessity  of  welding  part  to  part.  It  thus  hap- 
pens that  while  iron  boiler-plate  is  a  mass  of  heterogeneous 
constituent  elements,  and  liable  to  a  thousand  defects,  steel  is 
equally  remarkable  for  its  unity,  homogeneousness,  and  re- 
liability. 

When  an  iron  surface,  parallel  to  the  line  of  direction  of 
rolling  of  plates,  or  of  drawing  down  of  pieces  made  or  shaped 
under  the  hammer,  is  etched,  it  exhibits  plainly  the  lines  of 
"  fibre"  produced  by  the  drawing  out  of  the  cinder  originally 
present  in  the  puddle-ball,  and  reveals  any  defective  weld  or 
the  presence  of  any  mass  of  foreign  material.  When  a  cross- 
section  is  made,  as  in  the  cases  exhibited  in  the  preceding 
figures,  the  character  of  the  piling  is  shown,  and  also  that  ot 
the  workmanship.  In  these  examples,  which  are  reduced  to- 
one  half  the  size  of  the  originals,  Fig.  56  is  a  section  so  etched 
of  an  iron  locomotive  axle,  and  Fig.  57  of  a  steel  axle  of  similar 
7 


98 


THE   STEAM-BOILER. 


size  and  design.  The  beautiful  homogeneousness  of  good  steel 
is  exhibited  by  the  almost  perfect  uniformity  of  the  color  and 
texture  of  the  surface;  while  the  irregularity  both  of  color  and 
structure  of  the  other  illustration  reveals  plainly  the  reasons 
for  the  variable  wearing  quality  and  the  inevitable  uncertainty 
of  strength  which  must  always  attend  the  use  of  forged  iron, 
and  especially  when  made  of  "  scrap."  It  is  evidently  hope- 


FIG.  56. — LOCOMOTIVE  AXLE — 
"SPECIAL"  IRON. 


FIG.  57. — LOCOMOTIVE  AXLE — 
STEEL. 


less  to  secure  perfect  uniformity  of  structure,  texture,  and 
strength,  or  even  to  obtain  soundness,  where  such  great  num- 
bers of  welds  are  to  be  made,  and  where  so  much  impure  and 
foreign  material  is  distributed,  hap-hazard,  through  the  mass. 

42.  The  Methods  of  Test  of  iron  and  steel,  relied  upon 
to  reveal  the  properties  and  quality  of  the  metal,  are  becoming 
well  understood  and  standardized,  and  are  universally  practised 
in  all  important  work  by  experienced  and  skilful  engineers. 

Testing  Machines  are  used  for  testing  small  sections  and 
pieces  of  moderate  length.  They  are  usually  built  by  manu- 
facturers who  make  a  business  of  supplying  them  to  engineers 
and  other  purchasers,  and  are  generally  made  of  several  stand- 
ard sizes.  The  machine  is  frequently  fitted  up  to  test  both 
longitudinally  and  transversely ;  although  the  tests  generally 
made  are  in  but  one  direction.  The  Author  has  been  accus- 
tomed to  keep  in  use  a  machine  specially  intended  to  test  in 


MATERIALS— STRENGTH  OF   THE    STRUCTURE. 


99 


tension  and  compression,  and  also  separate  machines  for  trans- 
verse and  torsional  tests.  Tension-machine  is  shown  in  Fig. 
5  8:  it  consists  of  two  strong  cast-iron  columns,  secured  to  a 
massive  bed-frame  of  the  same  material ;  above  these  columns 
is  fastened  a  heavy  cross-piece,  also  of  cast-iron,  containing  two 
sockets,  in  which  rest  the  knife-edges  of  a  large  scale-beam. 
The  upper  chuck  is  suspended  by  eye-rods  from  knife-edges. 
All  the  knife-edges  are  tempered  steel,  and  the  sockets  and 


FIG.  58. — TENSION  TESTING-MACHINE. 

eyes  are  lined  with  the  same  material,  thus  reducing  friction  to 
r  minimum.  The  load  is  applied  by  means  of  a  screw,  or  by 
the  hydraulic  press,  with  a  fixed  plunger  and  movable  cylinder. 
The  stress  to  which  the  test-piece  is  subjected  is  measured  by 
means  of  suspended  weights  and  a  sliding  poise.  The  speci- 
men is  secured  in  the  chucks  either  by  wedge-jaws  or  bored 
chucks. 

The  extensions  are  measured  by  means  of  an  instrument 
(Fig.  59)  in  which  contact  is  indicated  by  an  "  electric  contact 
apparatus."  This  instrument  consists  of  two  accurately  made 


TOO 


THE   STEAM-BOILER. 


micrometer  screws,  working  snugly  in  nuts  secured  in  a  frame 
which  is  fastened  to  the  head  of  the  specimen  by  a  screw 

clamp.  It  is  so  shaped  that  the  mi- 
crometer screws  run  parallel  to  and 
equidistant  from  the  neck  of  the  spec- 
imen on  opposite  sides.  A  similar 
> frame  is  clamped  to  the  lower  head  of 
the  specimen,  and  from  it  project  two 
insulated  metallic  points,  each  opposite 
one  of  the  micrometer  screws.  Elec- 
tric connection  is  made  between  the 
c  two  insulated  points  and  one  pole  of  a 
voltaic  cell,  and  also  between  the  mi- 
crometer screws  and  the  other  pole. 
As  soon  as  one  of  the  micrometer 
screws  is  brought  in  contact  with  the 
opposite  insulated  point  a  current  is 

FIG.  59.— MEASURING  INSTRUMENT. 

established,  which  fact  is  immediately 

revealed  by  the  stroke  of  an  electric  bell  placed  in  the  circuit. 
The  pitch  of  the  screws  is  0.02  of  an  inch  (0.508  mm.),  and  their 
heads  are  divided  into  200  equal  parts ;  hence  a  rotary  advance 
of  one  division  on  the  screw-head  produces  a  linear  advance 
of  one  ten-thousandth  (o.oooi)  of  an  inch  (0.00254  mm.). 

A  vertical  scale,  divided  into  fiftieths  of  an  inch  (0.508  mm.), 
is  fastened  to  the  frame  of  the  instrument,  set  very  close  to 
each  screw-head  and  parallel  to  the  axis  of  the  screw ;  these 
serve  to  mark  the  starting  of  the  former,  and  also  to  indicate 
the  number  of  revolutions  made.  By  means  of  this  double  in- 
strument the  extensions  can  be  measured  with  great  certainty 
and  precision,  and  irregularities  in  the  structure  of  the  material, 
causing  one  side  of  the  specimen  to  stretch  more  rapidly  than 
the  other,  do  not  diminish  the  accuracy  of  the  measurements, 
since  half  the  sum  of  the  extensions  indicated  by  the  two  screws 
is  always  the  true  extension  caused  by  the  respective  loads. 

The  use  of  the  hydraulic  press  is  occasionally  found  to  bring 
with  it  some  disadvantages.  The  leakage  of  the  press  or  of  the 
pump  is  itself  objectionable,  and,  where  leakage  occurs,  it  is 
difficult  to  retain  the  stress  at  a  fixed  amount  during  the  time 


MA  TERIA  L S—  S  TRENG  TH   frF    Tli'E J  S  TRUCTVRE:  J      I O I 

required  in  the  measurement  of  extensions.  In  such  cases  ab- 
solute rigidity  in  the  machine  is  important,  and  the  stress  should 
be  applied  by  mechanism,  which  usually  consists  of  a  train  of 
gearing  operated  by  hand  or  by  power  transmitted  from  some 
prime  mover,  and  itself  operating  a  pulling  or  compressing 
screw,  as  in  Fig.  56. 

The  "  Autographic'  Testing-Machine  devised  by  the  Author 
is  used  where  it  is  desired  to  obtain  a  knowledge  of  the  general 
character  of  the  metal,  including  its  elasticity  and  resilience, 
and  the  method  of  variation  of  its  normal  series  of  elastic  limits, 
and  where  a  permanent  graphical  record  is  found  useful.  It  is 
shown  in  the  accompanying  figure. 

Fig.  61  is  a  perspective  view  of  this  machine.  It  consists  of 
two  A-shaped  frames  firmly  mounted  on  a  heavy  bed-plate. 
The  frames  are  secured  to  each  other  by  cross-bolts.  Near 
the  top  of  each  of  these  frames  are  spindles,  each  of  which 
has  a  head  with  a  slot  or  jaw  to  receive  and  hold  the  square 
heads  of  the  specimens.  The  two  spindles  are  not  connected 
to  each  other  in  any  way,  excepting  by  the  specimen  which  is 
placed  in  the  jaws  to  be  tested.  To  one  spindle  a  long  arm  is 
attached,  which  carries  a  heavy  weight  at  the  lower  end.  The 
other  has  a  worm-gear  wheel  attached  to  its  outer  end.  This 
wheel  is  driven  by  a  worm  on  the  shaft  which  is  turned  by  a 
hand  crank.  When  a  specimen  is  placed  in  the  two  jaws,  and 
the  spindle  is  turned  by  the  worm-gear,  the  effect  is  to  twist 
the  specimen  which  would  turn  the  spindle  ;  but  in  order  to  do 
this  the  weight  on  the  end  of  the  arm  must  be  swung  in  the 
direction  in  which  the  specimen  is  twisted.  But  the  farther 
the  arm  is  moved  from  a  vertical  position,  the  greater  will  be 
the  resistance  of  the  weight  to  the  turning  of  the  shaft,  while 
the  movement  of  the  arm  and  weight  is  effected  by  the  force 
-exerted  through  the  specimen  so  that  the  position  of  the  arm 
.and  weight  will  at  all  times  give  a  measure  of  the  torsional 
stress,  which  is  exerted  on  the  specimen  by  the  one  spindle, 
and  transmitted  by  the  former  to  the  other  spindle. 

But  as  this  torsional  stress  which  is  exerted  on  the  specimen 
is  increased,  it  will  at  once  commence  to  "give  way,"  or  be 
twisted  more  or  less  by  the  stress  according  to  the  quality  of 


102 


THE  'STEAM-BOILED. 


the  material.  In  making  such  torsional  tests,  it  is  essential  that 
we  should  know  how  much  the  specimen  was  twisted,  as  the 
strains  to  which  it  was  subjected  were  increased.  If  we  could 
procure  a  record  of  this,  it  would  be  an  indication  of  the  capac- 
ity of  the  material  to  resist  such  stresses,  or,  in  other  words,  of 
its  quality.  The  testing-machine  which  has  been  described 
was  designed  by  the  Author  for  this  purpose.  The  record  is 
made  in  the  following  way  :  To  one  spindle  a  cylindrical  drum 
is  attached,  which  is  covered  with  a  suitable  sheet  of  paper. 
To  the  pendulum,  is  attached  a  pencil,  the  point  of  which 
bears  on  the  paper  on  the  drum.  Now  supposing  that  the 
specimen  in  the  machine  should  offer  no  resistance,  but  should 
merely  twist,  the  pencil  would  then  remain  stationary,  and  as 
the  drum  is  revolved  the  pencil  would  trace  a  straight  line  on 


FIG.  60. — TEST-PIECE. 

the  paper,  the  length  of  which  line  would  measure  the  amount 
by  which  the  specimen  was  twisted.  If,  on  the  other  hand, 
a  specimen  be  supposed  to  resist  and  to  twist  simultaneously,, 
as  is  always  the  case,  then  it  will  presently  be  seen  that  the 
spindle  would  be  turned,  and  the  arm  with  the  weight  would 
be  moved  from  a  vertical  position  a  distance  proportional  to 
the  strain  resisted  by  the  specimen.  The  pencil-holder,  being 
attached  to  the  arm,  would  move  with  it.  As  explained  be- 
fore, the  distance  which  the  arm  and  its  weight  are  moved 
from  a  vertical  position  indicates  the  stress  on  the  specimen. 
Next,  in  order  to  make  a  record  of  this  distance,  a  "  guide- 
curve"  is  attached  to  the  frame  of  the  machine,  so  that  when 
the  pencil-holder  is  moved  out  of  the  vertical  position  the  pen- 
cil is  moved  toward  the  left  by  the  guide-curve,  which  is  of 
such  a  form  that  the  lateral  movement  which  it  gives  to  the 
pencil  is  proportional  to  the  moment  of  the  weight  on  the  end 


MATERIALS— STRENGTH  OF    THE    STRUCTURE.         1 03 

of  the  arm.  Now  suppose,  if  such  a  thing  were  possible,  that 
a  specimen  were  tested  which  would  not  "  give"  or  twist  at  all : 
in  that  case  the  spindles,  the  drum,  and  the  pencil  would  turn 
together,  or  their  movements  would  be  simultaneous,  so  that 
the  pencil  would  draw  a  vertical  line  along  the  paper.  But 


FIG.  61. — AUTOGRAPHIC  MACHINE. 

there  is  no  material  known  which  would  not  yield  or  twist 
more  or  less,  so  that  the  pencil  will  always  draw  some  form  of 
curved  line,  which  indicates  the  quality  of  the  material  tested. 
The  test-pieces  are  held  in  a  central  position  in  the  jaws  by 
lathe  "  centres,"  which  are  placed  in  suitable  holes  drilled  in  the 


1 04  THE   STEAM-BOILER. 

spindles  for  that  purpose.  The  specimen  is  then  held  securely 
by  wedges.  In  the  diagrams  each  inch  of  ordinate  denotes  100 
foot-pounds  of  moment  transmitted  through  the  test-piece,  and 
each  inch  of  abscissa  indicates  10  degrees  of  torsion.  The  fric- 
tion of  the  machine  is  not  recorded,  but  is  determined  when  the 
machine  is  standardized,  and  is  added  in  calculating  the  results. 

By  the  use  of  this  machine  the  metal  tested  is  compelled 
to  tell  its  own  story,  and  to  give  a  permanent  record  and 
graphical  representation  of  its  strength,  elasticity,  and  every 
other  quality  which  is  brought  into  play  during  its  test,  and 
thus  to  exhibit  all  its  characteristic  peculiarities. 

The  figures  on  page  105  are  derived  from  a  test  by  tension, 
as  made  for  the  Author.  On  page  106  is  given  the  record  of 
a  test  of  steel  made  by  the  Ordnance  Department,  U.  S.  A. 

43.  Tests  of  Strength  and  Ductility  of  irons  and  steels 
have  now  been  made  in  such  numbers,  and  with  such  a  variety 
of  composition,  that  the  engineer  designing  or  constructing 
boilers  need  have  no  doubt  in  regard  to  the  character  of  the 
metal  to  be  incorporated  in  the  structure. 

The  mean  of  a  considerable  number  of  experiments  on  ex- 
cellent American  iron  boiler-plate,  made  under  the  eye  of  the 
Author,  gave  a  tenacity  of  54,000  pounds  per  square  inch 
(3795.2  kilogs.  per  sq.  cm.)  with  a  variation  of  9  per  cent ; 
flange-iron  averaged  but  42,000  pounds  (2952.6  kgs.  per  sq.  cm.) 
with  a  variation  of  nearly  40  per  cent;  the  highest-priced, 
and  presumably  best,  plate  in  the  market  averaged  very  nearly 
60,000  pounds  (4218  kgs.),  varying  14  per  cent  ;  and  com- 
mon tank-iron  showed  practically  the  same  tenacity  and  varia- 
tion as  the  flange-iron,  and  less  ductility.  Thoroughly  good 
Pennsylvania  plate,  in  other  experiments,  gave,  for  all  good 
grades,  tenacities  not  ranging  much  from  55,000  pounds  per 
square  inch  (3866.5  kilogs.  per  sq.  cm.),  and  an  elastic  limit  at 
60  per  cent  of  the  ultimate  strength.  Such  tenacity  is  not 
usually  to  be  expected  when  buying  in  the  market,  and  it  is 
very  common,  when  designing  boilers  the  material  of  which  is 
not  prescribed,  for  the  designer  to  assume  that  its  tenacity  may 
not  exceed  40,000  pounds  (2812  kgs.).  On  the  other  hand,  a 
contract  and  specification  prescribing  careful  test  may  some- 


MATERIALS— STRENGTH   OF   THE   STRUCTURE. 


10$ 


TEST  OF  WROUGHT-IRON;    LENGTH  8"  (19.32  cm.),  DIAM.  0.798"  (2.03  cm.). 


LOADS. 

MICROMETER 
READINGS. 

EXTENSIONS. 

SETS. 

Actual. 

Per  sq.  in. 

Actual. 

Per  cent. 

Actual. 

Per  cent. 

150 
2,000 
4.OOO 
6,OOO 

8,000 

10,000 

150 

11.000 
12,000 

150 

13,000 

13,500 

14,000 

150 

15,000 

~  150 

17,000 

150 

19,000 

150 

21,000 

150 

22,000 

150 

22,500 
23,000 

23,500 
23,750 
21,800 

.6600 

.6628 

.6637 
.6646 
.  6606 
.6630 
.6600 
.6639 
.6700 
.6603 

.6715 
.6728 
.7242 
.7133 
•7535 
.7417 

.8474 
.8326 
.9720 
.9562 
.  1710 
.1524 
.3303 
.3102 

•4575 
.5610 
.7646 

Q.< 

9- 

•79!3 
.7910 
.7922 
•7930 
.7946 
.7948 
.7914 
•7951 
•7953 
.7915 
.7967 

•7959 
.8424 
•  8351 
.8712 
.8632 
.9618 
.9518 
.0856 
.0732 
.2811 
.2663 
.4381 
.4212 

•5441 
.6670 
.8693 
\1 
54 

4.000 
8,000 
12,000 
16.000 
20,000 

22.000 
24,000 

26,000 
27,000 
28,000 

•  0013 
.0023 
•0035 
.0050 
.0058 

.0064 
.0070 

.0080 
.0087 
•0577 

[0867 
.1790 
.3032 
.5004 
'.6586 

.016 
.029 
.044 
.063 
•073 

.030 
•037 

.100 

.  109 

.721 
1.084 
2.238 

3.790 
6.255 
8.233 

9.690 

11.105 
13.841 
18.375 

19.250 

.OOOI 
.0003 

.0486 
.0763 
!i666 
.2391 

•4337 
.6401 

.001 
.004 

.608 
.960 
2.083 

3-613 
6.043 
8.001 

30  ooo 

34.000 
38,000 

42,000 
44,000 

45,000 
46,000 
47,000 
47.500 
43,600 

•7752 
.8884 
1.0913 
1.4700 
1.5400 

Lbs. 
13,500 

ORIGINAL 
Lbs.  per 
sq.  in. 
47,500 

ELASTIC  LIMIT. 
ACTUAL. 
K               Lbs.  per      Kgs.  per 
sq.  in.            sq.  cm. 
6,140            27,000            1,898 

BREAKING  LOAD. 

SECT.                 FRACTURED  SECT. 
Kgs.  per         Lbs.  per      Kgs.  per 
sq.  cm.             sq.  in.           sq.  cm. 
3,340           69,840           4,910 

Ultimate    Elongation,    per     cent,    of 
length  =  19^. 
Reduction  of  Area,  per  cent,    =  31.99 
Modulus   of    Elasticity   =    24,365,000 
Ibs.  on  sq.  in. 
Modulus    of    Elasticity    =    1,712,860 
kilogrammes  on  sq.  cm. 

FINAL   DIMENSIONS. 
Length       =  9".  54 
Diameter  =  o".6s8 

io6 


THE   STEAM-BOILER. 


EXTENSION.  RESTORATION,  AND  PERMANENT  SET  OF  A  SOLID  CYLINDER 
OF  STEEL,  3  INCHES  LONG  (BETWEEN  SHOULDERS)  AND  0.622  INCH 
DIAMETER,  TAKEN  FROM  BREECH-RECEIVER  FOR  n-INCH  BREECH- 
LOADING  RIFLE. 


Weight 
per  s  quare 
inch  of 
Section. 

Extension 
per  inch 
in  Length. 

Successive 
Extension 
per  inch 
in  Length. 

Permanent 
Set 
per  inch 
in  Length. 

Successive 
Permanent 
Set  per  inch 
in  Length. 

Pounds. 

Inches. 

Inches.      Inches.      Inches. 

Inches. 

Inches. 

1,000 

0.00000 

o  .  ooooo      o  .  ooooo      o  .  ooooo 

0.00000 

o.  ooooo 

2,000 

.00000 

.  ooooo       .  ooooo       .  ooooo 

.ooooo 

.ooooo 

3,000 

.00000 

.  ooooo       .  ooooo       .  ooooo 

.00000 

.ooooo 

4,000 

.00033 

.00033 

.00033     .00033 

.ooooo 

.ooooo 

5.000 

.00033 

.ooooo 

.00033       .ooooo 

.00000 

.ooooo 

6,000 

.00033 

.00000 

.00033       .ooooo 

.ooooo 

.00000- 

7,000 

.00033 

.ooooo 

.00033   ,    .ooooo 

.00000 

.00000 

8,000 

.00033 

.00000 

.00033       .ooooo 

.ooooo 

.00000 

9,000 

.00033 

.ooooo 

.00033       .ooooo 

.00000 

.ooooa 

10,000 

.00033 

.ooooo 

.00033       .ooooo 

.ooooo 

.ooooo 

11,000 

.00033 

.ooooo 

.00033       .ooooo 

.00000 

.00000 

12,000 

.00033 

.00000 

.00033       .ooooo 

.ooooo 

.00000 

13,000 

.00033 

.ooooo 

.00033       .ooooo 

.00000 

.ooooo 

14,000 

.00033 

.00000 

.  00033       •  ooooo 

.00000 

.ooooo 

15,000 

.00033 

.ooooo 

.00033   1    .ooooo 

.00000 

.00000 

16,000 

.00067 

.00034 

.00067       .00034 

.ooooo 

.ooooo 

17,000 

.00067 

.ooooo 

.00067       .ooooo 

.00000 

.00000 

18,000 

.00067 

.ooooo 

.  00067       •  ooooo 

.00000 

.ooooo 

19,000 

.00133 

.00066 

.ooioo       -00033 

.00033 

.00033 

20,000 

.00233 

.00100 

.00100       .ooooo 

.00133 

.OOIOO- 

2I.OOO 

.00300 

.00067 

.00100          .00000 

.00200 

.00067 

22.000 

.00400 

.00100 

.OOIOO          .OOOOO 

.00300 

.00100 

23,OOO 

.00467 

.00067 

.00100 

.00000 

.00365 

.00067 

24,000 

•00533 

.00066 

.OOIOO 

.ooooo 

•00433 

.00066 

25,000 

.00633 

.00100 

.00133 

.00033 

.00500 

.00067 

26,000 

.00700 

.00067 

.00133 

.ooooo 

.00567 

.00067- 

27.000 

.00767 

.00067 

.00133 

.00000 

.00633 

.00066 

28,000 

.00900 

.00133 

.OOIOO 

—.00033 

.00800 

.00167 

29,OOO 

.00967 

.00067 

.00100 

.00000 

.00867 

.00067 

30,000 

.01067 

.00100 

.00133 

•00033 

.00933 

.00066 

31,000 

.01200 

.00133 

•00133 

.00000 

.01067 

.00134 

32,000 

.01300 

.00100 

.00167 

.00034 

.01133 

.00066 

33,000 

•01433 

.00133 

.00167 

.00000 

.01267 

.00134 

34.000 

.01567 

•00134 

.00133 

—.00034 

•01433 

.00166 

35,000 

.01700 

.00133 

.00133 

.ooooo 

.01567 

.00134 

36,010 

.OlSoO 

.00100 

•00133 

.00000 

.01667 

.00100 

37,000 

.01967 

.00167 

.00133 

.00000 

•01833 

.00166 

38,000 

•02133 

.00166 

.00167 

.00034 

.01967 

.00134 

39,000 

•02433 

.00300 

.00167 

.ooooo 

.02267 

.00300 

40,000 

•02567 

.00134 

.00167 

.ooooo 

.02400 

.00133 

41,000 

•02733 

.00166 

.00167 

.ooooo 

•02567 

.00167 

42,000 

.02867 

.00134 

.00167 

.00000 

.02700 

.00133. 

43,000 
44.000 

•03033 
.03300 

.00166 

.00267 

.00200 

.00233 

.00033 
.00033 

•02833 
.03067 

.00133. 
.00234 

45.000 

•03433 

.00133 

.00200 

—.00033 

•03233 

.00166 

46,000 

.03900 

.00467 

•00233 

.00033 

.03667 

.00434 

47,000 

.04167 

.00267 

.02223 

.ooooo 

•03933 

.00266 

48,000 

.04367 

.00200 

.00233 

.00000 

•04133 

.00200 

49,000 

.04700 

.00333 

.00267 

.00034 

•04433 

.00300 

50,000 

.05100 

.00400 

.00200 

—  .00067 

.04900 

.00467 

51,000 

•05533 

•00433 

.00300 

.00100 

•05233 

.00333. 

52,000  . 

.06067 

•00534 

.00233 

—  .00067 

•05833 

.  00600 

53,000 

.06667 

.00600 

.00300 

.00067 

.06367 

•00534 

54.000 

.06897 

.00200 

.00233 

—  .00067 

.06633 

.00266 

55,ooo 

.07867 

.01000 

.00300 

.00067 

•07567 

.00934 

56.000 

•08333 

.00466 

.001500 

.oocoo 

.08033 

.00466 

57.000 

.09500 

.01167 

.00300 

.ooooo 

.09200 

.01167 

58,000 

.10233 

•00733 

.00333 

.00033 

.09900 

.00700 

59,000 

.IISOO 

.01567 

.00333 

.00000 

.11467 

.01567 

60,000 

.13700 

.01900 

.00367 

.00034 

•13333 

.01866 

61,000 
62.000 

.16900 
0.30367 

.03200 

0.13467 

0.00400 

1   (*) 

0.00033 
(*) 

0.16500 

(*) 

0.03.67 

Tensile  Strength  per  sq.  in Ibs.    62,000 


*  Specimen  broke. 
GENERAL  SUMMARY. 


Elastic  limit 


Ibs. 


19,000 


Extension  per  in.  at  elastic  limit in.  0.00133 

Extension  per  in.  at  rupture in.  0.30367 


Original  area  of  cross-section.,  .sq.  in.    0.3038 

Area  after  rupture sq.  in.    0.1611 

Position  of  rupture ^  from  shoulder. 

Character  of  fracture Fibrous. 


MATERIALS— STRENGTH    OF    THE   STRUCTURE.         IO/ 

times  secure  iron,  if  thin,  capable  of  sustaining  60,000  pounds  per 
square  inch  (4218  kilogs.  per  sq.  cm.).  A  fair  contract  figure,  and 
one  that  may  be  assumed  in  designing  when  the  iron  is  to  be 
thus  selected  and  tested,  would  be  considered  to  be  55,000 
pounds  (3867  kilogs.). 

Steel  boiler-plate  of  high  tenacity  is  so  certain  to  involve  in 
its  use  risk  of  cracking,  either  in  the  process  of  construction,  or 
later,  after  exposure  to  variations  of  temperature,  and  to  alter 
so  seriously  and  so  uncertainly  in  all  its  physical  properties, 
that  specifications  usually  prescribe  that  it  shall  not  exceed 
60,000  pounds  (4218  kilogs.)  tenacity,  and  in  some  cases  the 
figure  is  put  even  lower.  When  first  introduced,  tenacities 
much  greater  were  allowed  for  steels,  and  great  risks,  and  often 
serious  accidents  and  losses  of  life  and  property,  were  the  conse- 
quence. All  good  boiler-irons  should  be  expected  to  stretch  at 
least  20  per  cent  of  the  length  of  the  test-piece,  the  latter  being 
made  at  least  four  or  five,  and  better  eight  or  ten,  diameters, 
or  breadths  in  length.  The  best  irons  stretch  25  per  cent,  and 
the  best  steels  even  more.  Thick  plates  have  less  tenacity  and 
less  ductility  than  thin. 

The  "  bending  test "  is  one  which  only  the  best  of  irons  and 
the  softer  steels  will  bear.  The  strip  cut  from  the  sheet  for 
test,  the  "  coupon"  as  it  is  called,  if  of  less  than  f  inch  thick- 
ness, should  bend  completely  over  and  be  hammered  flat  upon 
itseU,  as  in  the  figure. 


FIG.  62. — BENDING  TEST. 

Steels  subjected  to  the  "  temper  test,"  by  heating  the  sam- 
ple red-hot  and  quenching  in  cold  water,  should  then,  if  of 
good  quality  for  boilers,  be  capable  of  successfully  passing  the 
bending  test ;  but  it  is  not  usually  demanded  that  it  shall  close 
down  flat.  If  it  bends  to  a  circle  of  a  diameter  less  than  three 
times  its  own  thickness,  it  is  accepted.  Steels  subjected  to  the 
"  drifting  test "  are  commonly  drilled  with  a  -f-inch  drill,  and 
the  hole  drifted  out  as  large  as  possible.  If  it  is  enlarged  to 


108  THE   STEAM-BOILER. 

double  its  original  diameter,  the  metal  is  usually  accepted ; 
but  it  is  sometimes  demanded  that  it  shall  bear  extension  to 
two  inches  in  diameter,  as  for  example  at  Crewe,  on  the  Lon- 
don and  Northwestern  Railway  of  Great  Britain. 

44.  Specifications  of  Quality,  as  well  as  of  kind  and  form, 
of  materials  proposed  to  be  used  in  steam-boiler  construction 
are  so  drawn  as  to  secure  not  only  an  understanding  on  the  part 
of  the  maker  or  vender  of  the  exact  nature  of  the  intended 
provisions,  but  also  a  means  of  certainly  determining  whether 
those  specifications  and  the  contract  are  fully  complied  with. 

Wrought-iron  and  steel,  as  has  been  seen,  are  very  variable 
in  strength  and  other  qualities.  For  small  iron  parts,  a  tenacity 
of  55,000  to  60,000  pounds  per  square  inch  (3867  to  4218  kilo- 
grammes per  square  centimetre)  is  usually  called  for ;  but  the 
strength  of  plate  or  of  large  masses  is  rarely  three  fourths  as 
great.  The  specification  usually  calls  for  "  iron  of  the  best 
quality,"  tough,  of  a  definite  tenacity,  fibrous,  free  from  cinder- 
streaks,  flaws,  lamination  or  cracks,  uniform  in  quality,  and 
with  a  prescribed  elastic  limit,  and  often  a  stated  modulus  of 
elasticity.  Even  the  method  of  piling,  heating,  and  rolling  or 
hammering  is  specified. 

As  has  been  shown  fully  in  the  preceding  chapters,  the  di- 
mensions must  be  determined  after  a  careful  consideration  of 
the  character  and  the  method  of  application  of  the  load,  as 
well  as  of  its  magnitude,  and  allowance  must  be  made  by  the 
engineer  for  the  effect  of  heat  or  cold,  of  repeated  heating  in 
the  process  of  manufacture,  for  the  rate  of  set  under  load,  for 
the  rapidity  of  its  application,  or  for  the  effect  of  repeated  or 
reversed  strains. 

The  differences  in  the  behavior  of  the  several  kinds  of  iron 
or  steel  under  the  given  directions  must  be  considered  in  pro- 
portioning parts.  Thus  unannealed  iron  or  "low"  steel  will  be 
chosen  for  parts  exposed  to  steady  and  heavy  loads ;  the  use  of 
annealed  metal  will  be  restricted  to  cases  in  which  the  primary 
requisite  is  softness  or  malleability  ;  steel  containing  about  0.8 
per  cent  carbon  will  be  given  the  preference  for  parts  exposed 
to  moderate  blows  and  shocks  which  are  not  expected  to  ex- 
ceed the  elastic  resilience  of  the  piece ;  tough,  ductile  metal, 


MATERIALS— STRENGTH  OF   THE   STRUCTURE.         1 09 

preferably  "  ingot  iron,"  will  be  chosen  for  parts  exposed  to 
shocks  capable  of  producing  great  local  or  general  distortion. 

"  Wohler's  Law"  dictates  the  adoption  of  increased  factors 
of  safety,  or  of  some  equivalent  device,  as  Launhardt's  formula, 
when  variable  loads  are  carried.  Thus  the  engineer  is  com- 
pelled to  make  a  specification,  in  very  important  work,  which 
shall  prescribe  all  the  qualities  of  materials  and  exactly  the 
proportions  of  parts  needed  to  make  his  work  safe  for  an  in- 
definite period. 

Steel  has  such  a  wide  range  of  quality  that  few  difficulties 
are  met  with  in  its  introduction  into  any  department  of  con- 
struction. In  boiler-work,  however,  it  must  be  kept  low  in  car- 
bon, and  therefore  in  tenacity ;  and  in  machinery  and  bridge 
work,  also,  its  composition  must  be  carefully  determined  upon, 
and  as  exactly  specified. 

The  following  are  good  specifications  for  boiler-work : 

Steel  Sheets. — Grain — To  be  uniform  throughout,  of  a  fine 
close  texture.  Workmanship — Sheets  to  be  of  uniform  thick- 
ness, smooth  finish,  and  sheared  closely  to  size  ordered.  Tensile 
Strength — To  be  60,000  pounds  to  square  inch  for  firebox 
sheets,  and  55,000  pounds  for  shell  sheets.  Working  Test — A 
piece  from  each  sheet  to  be  heated  to  a  dark  cherry  red,  plung- 
ed into  water  at  60°,  and  bent  double,  cold,  under  the  hammer; 
such  piece  to  show  no  flaw  after  doubling. 

Iron  Sheets. — Grain — To  be  uniform  throughout,  showing 
a  homogeneous  metal  with  no  layers  or  seams.  Workmanship 
—Sheets  to  be  of  uniform  thickness,  smooth  finish,  and  sheared 
closely  to  size  ordered.  Tensile  Strength — To  be  60,000  pounds 
to  the  square  inch  for  firebox  sheets,  and  55,OOO  pounds  for 
shell  sheets.  Working  Test — A  piece  from  each  sheet  to  be 
bent  cold  to  a  right  angle,  showing  no  fracture.  A  piece  bent 
double,  hot,  to  show  no  flaking  or  fracture. 

Specifications  for  Boiler  Tubes. — Size — Locomotive  tubes 
to  be  12  feet  long  and  2  inches  diameter;  to  be  of  iron,  No. 
ii  gauge.  Quality  of  Metal — When  flattened  under  the  ham- 
mer to  show  tough  fibrous  grain ;  when  polished  and  etched 
with  acid  to  show  uniform  metal  and  a  close  weld.  Working 
Tests — When  expanded  and  beaded  into  the  flue-sheet  to  show 


110  THE.  STEAM-BOILER. 

no    flaws;   to  stand  "swaging   down"  hot   without    flakes    or 
seams. 

The  following  are  specifications  for  Boiler  and  Firebox  Steel : 

(1)  A  careful  examination  will  be  made  of  every  sheet,  and 
none  will  be  received  that  show  mechanical  defects. 

(2)  A  test  strip  from  each  sheet,  tested  lengthwise. 

(3)  Plate    will    not    be    passed    for    acceptance    when    of 
strength  of  less  than  50,000  or  greater  than  65,000  pounds  per 
square  inch,  nor  if  the  elongation  falls  below  twenty-five  per 
cent. 

(4)  Should  any  sheets  develop  defects  in  working  they  will 
be  rejected. 

(5)  Manufacturers  must  send  one  test  strip  for  each  sheet 
(this  strip  must  accompany  the  sheet  in  every  case),  both  sheet 
and  strip   being  properly   stamped  with  the  marks  designated 
by  the  company,  and  also  lettered  with  white  lead,  to  facilitate 
marking. 

The  U.  S.  Board  of  Supervising  Inspectors  of  Steam-vessels 
restrict  the  stress  on  boiler  stays  and  braces  to  6000  pounds 
per  square  inch  (4218  kilogrammes  per  square  centimetre).  For 
shells  of  boilers,  a  factor  of  safety  of  6  is  permitted  in  design- 
ing. The  hydrostatic  pressure  applied  in  testing  is  one  half 
greater  than  the  steam-pressure  allowed.  All  plates  must  be 
stamped  by  the  maker  with  the  tenacity,  as  determined  by  test, 
at  the  four  corners  and  in  the  middle.  The  elongation  is  not 
noted,  as  the  form  of  United  States  standard  test-piece  is 
unfitted  to  determine  it.  The  contraction  of  area  of  section  at 
fracture  must  be  0.15  when  the  tenacity  is  45,000  pounds  and 
one  per  cent  more  for  each  additional  1000  pounds. 

Hot-short,  or  red-short,  and  cold-short  irons  are  detected  by 
the  forge  tests ;  the  former  is  often  found  to  be  an  excellent 
quality  of  iron  if  it  can  be  worked  into  shape,  as  it  is,  when  cold, 
tough  and  strong.  Specially  high  qualities  are  rarely  economi- 
cal, as  they  usually  cost  too  much  to  make  the  difference  worth 
what  is  paid  for  it.  Shapes  difficult  to  make  or  roll  are  usually 
weaker  than  others.  Mills  will  usually  supply  "  pattern  iron," 
charging  a  little  extra  for  it ;  but  it  will  often  be  found  economi- 
cal to  order  them,  if  such  shapes  are  necessary.  In  designing, 


MA  TERIAL S— STRENGTH  OF   THE   STRUCTURE.         Ill 

however,  it  is  well  to  avoid  the  introduction  of  peculiar  shapes, 
if  possible. 

All  wrought-iron,  if  cut  into  testing  strips  one  and  a  half 
inches  in  width,  should  be  capable  of  resisting  without  signs  of 
fracture,  bending  cold  by  blows  of  a  hammer,  until  the  ends  of 
the  strip  form  a  right  angle  with  each  other,  the  inner  radius  of 
the  curve  of  bending  being  not  more  than  twice  the  thickness  of 
the  piece  tested.  The  hammering  should  be  only  on  the  ex- 
tremities of  the  specimens,  and  never  where  the  flexion  is  tak- 
ing place.  The  bending  should  stop  when  the  first  crack  ap- 
pears. 

All  tension  tests  should  be  made  on  a  standard  test-piece  of 
one  and  a  half  inches  in  width,  and  from  one  quarter  to  three 
quarters  of  an  inch  in  thickness,  planed  down  on  both  edges 
equally  so  as  to  reduce  the  width  to  one  inch  for  a  length  of 
eight  inches.  Whenever  practicable,  the  two  flat  sides  of  the 
piece  should  be  left  as  they  come  from  the  rolls.  In  all  other 
cases  both  sides  of  the  test-piece  are  planed  off.  In  making 
tests  the  stresses  should  be  applied  regularly,  at  the  rate  of 
about  one  ton  per  square  inch  in  fifteen  seconds  of  time. 

All  plates,  angles,  etc.,  which  are  to  be  bent  in  the  manu- 
facture should,  in  addition  to  the  above  requirements,  be 
capable  of  bending  sharply  to  a  right  angle  at  a  working  test, 
without  showing  any  signs  of  fracture. 

All  rivet-iron  should  be  tough  and  soft,  and  pieces  of  the 
full  diameter  of  the  rivet  should  be  capable  of  bending  until 
the  sides  are  in  close  contact,  without  showing  fracture. 

All  workmanship  should  be  first-class;  all  abutting  surfaces 
planed  or  turned,  so  as  to  insure  even  bearing,  taking  light  cuts 
so  as  not  to  injure  the  end  fibres  of  the  piece,  and  protected  by 
white  lead  and  tallow.  Pieces  where  abutting  should  be  brought 
into  close  and  forcible  contact  by  the  use  of  clamps  or  other 
approved  means  before  being  riveted  together.  Rivet-holes 
should  be  carefully  spaced  and  punched,  and  in  all  cases  reamed 
to  fit,  where  they  do  not  come  truly  and  accurately  opposite, 
without  the  aid  of  drift-pins.  Rivets  should  completely  fill  the 
holes,  and  have  full  heads,  and  be  countersunk  when  so  required. 

The  following   are   specifications  originally  issued  by  the 


112  THE   STEAM-BOILER. 

United  States  Navy  Department,  which  indicate  the  relation 
of  variation  of  tenacity  to  the  corresponding  change  in  ductil- 
ity where  the  quantity  of  carbon  in  steel  is  altered : 

TENACITY. 

EXTENSION. 


Lbs.  per  sq.  in.  Kilos,  per  sq.  cm.  Per  cent. 
6o,OOO                                 4218  25 

7O,OOO  4921  23 

8o,OOO  5624  19 

9O,OOO  6327  12 


A  cold-bending  test  is  demanded  thus:  Bend  the  strip  over 
a  mandrel  of  a  diameter  i^  times  the  thickness  of  the  plate, 
through  an  arc  of  90°,  and  no  cracks  must  appear  with  the 
softer  grades,  and  any  cracks  seen  in  the  case  of  the  harder 
steels  must  be  insignificant. 

Every  reputable  maker  stamps  his  iron,  not  only  with  the 
figures  indicating  the  tenacity,  as  required  by  law,  but  also,  in 
the  case  of  thoroughly  good  qualities,  with  their  names.  Where 
the  brand  is  not  found,  it  is  assumed  by  the  experienced  en- 
gineer that  the  metal  is  not  of  such  high  quality  as  to  do  credit 
to  the  maker.  All  good  plate  is  expected  to  have  fair  tenacity 
and  high  ductility,  and  good  flange-iron  should  not  deteriorate 
appreciably  in  working. 

45.  Choice  of  Quality  of  Metal  for  the  Various  Parts 
of  a  boiler  or  other  structure  is  made  with  the  greatest  care  by 
the  designer  and  by  the  constructor.  The  furnace,  exposed  as 
it  is  to  variations  of  temperature,  to  the  corrosive  effect  of  hot 
gases,  and  to  the  mechanical  wearing  action  of  the  cinder  and 
coal  carried  by  their  rapidly  moving  currents,  is  made  of  the 
harder  qualities  of  iron  or  steel  already  described.  The  tubes, 
flues,  and  the  flue-sheets  are  composed  of  comparatively  ductile 
material,  such  as  may  be  safely  shaped  in  accordance  with  the 
plans  of  the  designer ;  the  shell  may  be  of  cheaper  material ; 
while  all  stays  and  braces  must  be  made  of  the  strongest  and 
toughest  metal  available.  Each  grade  should  be  carefully  pre- 
scribed, and  the  iron  or  steel  proposed  for  use  as  carefully  in- 
spected and  tested  before  it  is  introduced  into  the  structure. 
It  is  sometimes  advisable  to  substitute  copper  for  iron,  espe- 


MATERIALS— STRENGTH  OF    THE   STRUCTURE.         11$ 

cially  in  the  firebox ;  and  in  such  cases  sheet-copper  of  a  tena- 
cious and  somewhat  hard  quality  should  be  adopted.  This  ma- 
terial usually  has  about  two  thirds  the  strength  of  good  iron, 
with  greater  ductility  and  flexibility,  and  resists  the  action  of 
the  furnace  gases  better  than  iron  boiler-plate. 

46.  The  Methods  of  Working  the   materials  introduced 
into  steam-boilers  are  adapted  very  carefully,  in  every  case,  to 
the  known  requirements  of  each  quality  so  used.    The  frequent 
injury  of  steel  and  of  hard  iron  plates  by  punching  and  by  too 
abrupt    change   of    form   have   led    engineers    to    prescribe   in 
many  cases  that  all  steel  plate  shall  be  drilled  for  the  insertion 
of  rivets,  and   not  punched,  and  to  direct  the  bending  of  the 
plate  over  rounded  edges  having  comparatively  large  radii  of 
curvature.     All  wrought-iron  work  in  boilers,  when  subjected 
to   any  considerable   change   of  form,  should  be  worked  at  a 
bright-red  heat,  approaching   the  welding  temperature ;   steel 
should  be  handled,  in  such  cases,  at  a  "  cherry-red  "  heat. 

Great  alteration  of  shape,  if  effected  at  ordinary  tempera- 
tures, should  be  made  slowly  and  carefully,  and  it  may  even  be 
well  in  some  instances  to  allow  intermissions  in  such  opera- 
tions sufficient  to  permit  the  particles  some  opportunity  of 
self-adjustment.  It  may  be  taken  as  a  general  rule  in  the  work- 
ing of  all  materials  for  steam-boilers,  that  the  methods  and  pro- 
cesses chosen  should  always  be  such  as  will  be  least  likely  to 
strain  or  to  injure,  either  generally  or  locally,  the  iron  or  steel 
so  used. 

47.  Special  Precautions  in  Using  Steel  are  found  to  be 
necessary  to   secure  safe  construction.     Construction   in  steel 
demands  more  care  than  the  making  of  iron  boilers,  and  a  good 
boiler-maker  for  the   latter  class  of  work  is  not  necessarily  a 
good  worker  of  steel.    In  handling  steel  for  boilers  there  should 
be   no  unnecessary  local  heating.      If  so  heated,  steel  should 
always  be  subsequently  annealed.     The  plates  for  the  cylindri- 
cal  shells  of  boilers  should   be  carefully  bent  to  shape  when 
cold.     The  rivet-holes  should  usually  be  drilled,  not  punched, 
and  the  drilling  should  be  done  after  the  plates  are  bent  to 
shape,    and    bolted    together    in    position.      The   longitudinal 
joints  in  the  shell  are  best  made  with  double  butt-strips,  one 


U4  THE    STEAM-BOILER. 

being  placed  inside,  and  the  other  outside,  to  form  a  "  butt 
joint." 

The  tests  of  the  plate  supplied  on  specifications,  and  under 
contracts,  should  be  even  more  carefully  and  minutely  made 
than  with  iron ;  every  operation  must  be  more  carefully  con- 
ducted and  supervised,  and  the  completed  boiler  should  be 
inspected  and  tested  with  the  greatest  possible  care.  If  it  is 
well  made  and  of  good  material,  it  will  be  a  more  satisfactory 
construction  than  any  iron  boiler  can  possibly  be ;  a  mistake  in 
accepting  and  using  steel  ill  adapted  to  the  purpose  may 
produce  an  exceedingly  dangerous  and  unsatisfactory  boiler. 
Steel  of  good  quality,  and  well  adapted  for  other  construction, 
is  not  necessarily  safe  for  use  in  steam-boilers. 

Many  engineers  would  anneal  every  plate  of  steel  used, 
whatever  its  apparent  quality,  to  insure  its  safety  in  the  struc- 
ture, and  it  has  even  been  suggested  that  it  would  be  well,  were 
it  practicable,  to  anneal  the  whole  boiler  after  completion.* 
Too  great  care  cannot  be  taken  in  selecting  the  metal. 

48.  Rivets  and  Rivet-Iron  and  Steel  are  necessarily  of 
especially  good  quality.  The  rivet  must  be  strong,  tough,  and 
ductile,  and  capable  of  bearing  the  severest  deformation  at  all 
temperatures  without  injury.  It  is  customary  to  "  head-up" 
rivets  hot ;  but  medium-sized  and  small  rivets,  in  some  locali- 
ties, are  worked  cold,  and  this  is  the  most  trying  test  of  quality 
possible.  Rivets  of  less  than  f-inch  (0.95  cm.)  diameter  are 
very  commonly  driven  cold.  Rivet-iron  should,  in  the  bar, 
have  a  tenacity  approaching  60,000  pounds  per  square  inch 
(4218  kgs.  per  sq.  cm.),  and  should  be  as  ductile  as  the  very 
best  boiler-plate  when  cold.  The  rivet  should  be  capable  of 
bearing  the  change  of  form  incidental  to  its  use  without  ex- 
hibiting a  tendency  to  split ;  the  head  should  not  seriously 
harden  or  become  brittle  under  the  blows  of  the  hammer  ;  and 
the  contraction  on  cooling,  after  it  has  been  headed  up,  should 
not  cause  weakening  by  the  stress  incident  to  the  strain  so 
produced.  A  good  iron  rivet  f  inch  (1.6  cm.)  diameter  can  be 
doubled  up  and  hammered  together,  cold,  without  exhibiting 

*  Trans.  Am.  Soc.  M.  E.,  1887,  No.  ccxlvi. 


1889]  THE    LOCOMOTIVE. 


PRINTING  HOUSE  (68).  A  boiler  exploded  in  a  printing  and  publishing  house  in 
Cincinnati,  on  May  23d.  Further  particulars  of  this  explosion  are  given  in  our  Cincinnati 
letter  in  this  issue. 

STEAM  SHOVEL  (69). — On  May  25th,  -while  three  men  were  engaged  at  work  in  the 
engine  room  of  the  steam  shovel  which  is  being  used  for  loading  ballast  on  the  cars  at 
Wales,  Out.,  for  grading  purposes  on  the  Grand  Trunk  Railway  double  track,  the  boiler 
exploded,  seriously  injuring  two  of  the  men,  one  of  whom,  Mclntosh,  is  expected  to  die. 

PORTABLE  SAW-MILL  (70).  —  The  boiler  of  Gilfilen  &  Gibson's  portable  saw-mill,  situ- 
ated on  Poindexter's  creek,  near  Winfield,  W.  Va.,  blew  up  on  the  morning  of  May  31st, 
with  terrific  force.  William  Doss  was  instantly  killed  ;  George  Gilfilen  died  two  days  later 
from  a  crushed  skull,  broken  collar  bone,  and  other  injuries  ;  Burns  Wooten  was  badly 
bruised  and  scalded,  and  cannot  recover  ;  David  Chambers,  the  sawyer,  received  several 
injuries  about  the  body  and  head,  none  of  which  are  serious.  Several  of  John  Gibson's 
bones  were  broken,  and  he  was  otherwise  seriously  but  not  dangerously  hurt.  One  of  John 
Niberl's  eyes  was  blown  out,  and  he  was  badly  burned  about  the  body.  The  lumber  inspector 
of  the  McLaughlin  Timber  Company,  of  Columbus,  O  ,  happened  to  be  on  the  grounds,  and 
was  seriously  hurt.  Engineer  Wolford,  who  was  slightly  injured,  fled  to  the  woods  after 
the  accident,  and  Has  not  been  seen  since.  About  five  feet  of  that  portion  of  the  boiler  to 
which  the  fire-box  is  attached  was  blown  about  one  hundred  feet  in  the  air,  coming  down 
about  one  hundred  yards  from  the  mill,  imbedding  itself  into  the  ground  three  feet.  The 
mill,  which  is  estimated  to  have  been  worth  two  thousand  dollars,  is  a  total  wreck. 


On  the  Longitudinal  Riveted  Joints  of  Steam-Boiler  Shells.* 

BY   JOHN   H.    COOPER,    PHILADELPHIA,    PA. 

The  initial  statement  to  the  English  Lloyd's  rules  for  steam-boilers  is  embodied  in  the 
following  words  :  "  The  strength  of  circular  shells  to  be  calculated  from  the  strength  of 
longitudinal  joints,"  which  assures  us  that  this  part  of  the  boiler  should  be  properly  pro- 
portioned. To  these  rules  a  memorandum  is  added  :  "  In  any  case  where  the  strength  of 
the  longitudinal  joint  is  satisfactorily  shown  by  experiment  to  be  greater  than  given  by  this 
formula  (Lloyd's),  the  actual  strength  may  be  taken  in  the  calculation."  Later  on,  Lloyd's 
rules  (under  the  head  of  "  Periodical  Surveys,"  regarding  the  examination  of  boilers  after 
they  have  been  several  years  in  service)  say  :  "The  safe  working  pressure  is  to  be  deter- 
mined by  their  actual  condition."  These  statements  lie  in  the  line  of  practical  efficiency, 
and  point  to  the  necessity  of  providing  material  in  accordance  with  the  requirement  of  the 
load  to  be  carried. 

Any  one  who  takes  the  trouble  to  collect  and  compare  data  on  this  subject  cannot  fail 
to  notice  the  great  disparity  of  rules  for  determining  the  working  pressure  permissible  for 
boilers.  The  case  is  clear  by  simple  reasoning  on  the  data  collected,  that  boilers  are  held 
together,  it  would  seem,  more  by  conformity  to  rule  than  by  the  materials  of  which  they 
are  made.  But  of  course  the  true  course  to  pursue  is  to  give  to  each  member  its  proper 
allowance  of  section,  in  order  that  the  components  of  the  joint  shall  have  an  equal  chance 
under  strain  according  to  its  resisting  power.  The  diminished  strength  of  the  shell  of  a 
boiler  by  a  longitudinal  joint  is  well  known,  and  it  becomes  good  engineering  so  to  propor- 
tion its  parts  as  to  obtain  the  greatest  strength  possible  within  the  limits  of  practical 
economy. 

When  it  became  necessary  to  assure  themselves  confidently  of  the  permanent  safety  of 
a  structure  composed  of  plates  held  together  by  rivets,  engineers  were  not  long  in  finding 
out  that  a  certain  allotment  of  rivet  section  to  plate  section  at  the  joints  was  necessary,  and 
that  these  sections  were  found  to  be  nearly  equal  in  the  strongest  joints.  The  experiments 


*  Communicated  to  the  LOCOMOTIVE  by  the  author. 


102  THE    LOCOMOTIVE.  [JULY, 

of  Fairbairn,  conducted  in  the  year  1838,  proved  that  —  "  the  sectional  area  of  the  rivets  in 
a  joint  was  nearly  equal  to  the  sectional  area  of  the  plate  through  the  rivet  holes."  Subse- 
quent experiments  by  Clark  on  riveted  plates  for  the  Britannia  and  Conway  Tubular  Bridge 
fully  corroborate  the  above  statement;  his  conclusion  was:  "The  collective  area  of  the 
rivets  is  equal  to  the  sectional  area  of  the  plate  through  the  rivet-holes."  This  relation  of 
the  components  of  the  joint  in  course  of  time  became  embodied  in  the  English  Board  of 
Trade  rules  and  in  Lloyd's  rules  now  in  force,  regulating  the  construction  of  steam-boilers. 
It  also  forms  the  basis  of  the  Philadelphia  steam-boiler  inspection  ordinance,  first  formu- 
lated in  1882. 

Referring  now  to  those  rules  only  which  relate  to  the  proportions  of  the  longitudinal 
joints  of  the  cylindrical  shells  of  boilers,  we  are  prepared  to  say  they  may  be  most  con- 
veniently presented  b}'  the  following  notation  and  formulae  : 

A  =  Percentage  'of  punched  plate  to  the  solid  plate. 
B  =  Percentage  of  driven  rivet  section  to  the  solid  plate. 
C  '  —  The  pressure  in  Ibs.  per  square  inch  which  the  boiler  is  allowed  to  carry. 
a  =  Area  of  driven  rivet,  or  rivet  -hole. 
d  =  Diameter  of  rivet-hole. 
n  =  Number  of  rows  of  rivets. 
p  —  Pitch  of  rivets. 
t  =  Thickness  of  plates. 
R-  Radius  of  boiler  shell. 

8—  Ultimate  shearing  strength  of  rivets  in  Ibs.  per  square  inch  of  section. 
T—  Ultimate  tensile  strength  of  plates  in  Ibs.  per  square  inch  of  section. 
/  =  Factor  of  safety. 

E—  Limit  of  elasticity  in  the  plates  in  Ibs.  per  square  inch. 
%  =  Percentage  of  joint  strength. 

The  least  of  A  or  B  should  be  inserted  in  the  formula  for  finding  C.  All  dimensions 
are  in  inches.  The  notation  and  the  formulae  mutually  explain  each  other. 

p  —  d 

A  =  -          .....        (1), 
P 

a  n 

B  =  -          .....       (2), 
pt 

t  (A  or  B)  T 


These  formulae  are  intended  exclusively  for  the  guidance  of  the  inspector  in  ascertain- 
ing the  exact  strength  of  the  joints  in  the  boilers  which  come  under  his  care,  and  which 
enable  him  to  determine  the  working  pressure  of  steam  allowable  under  the  rules.  They 
do  not,  however,  enable  the  boiler-maker  to  determine  directly  that  proportion  of  pitch 
which  he  should  use  with  any  given  plate  thickness  and  rivet  diameter,  in  order  to  secure 
the  strongest  joint  and  which  will  also  pass  the  highest  inspection.  To  secure  these 
results,  the  following  simple  formulae  were  devised  by  the  writer  (early  in  1882),  in  which 
the  notation  given  above  is  similarly  employed,  and  which  may  be  thus  expressed.  For 
single  riveted  joints,  when  iron  plates  are  secured  by  iron  rivets  and  when  the  plate  thick- 
ness and  rivet  diameter  are  given,  it  is  desired  to  find  a  pitch  that  will  secure  equality  of 
plate  and  rivet  section  —  the  formulae  will  be  : 

p  =  —  +  d.        .        .        .        .       (4). 
This  plainly  means  that  the  pitch  is  equal  to  the  area  of  the  rivet  hole,  divided  by  the 


1889.]  THE    LOCOMOTIVE.  103 


thickness  of  the  plate,  and  to  the  result  of  which  the  diameter  of  the  rivet  hole  must  be 
added. 

For  multiple  riveted  joints,  when  iron  plates  are  secured  by  iron  rivets,  the  same 
formula  is  used  with  the  addition  only  of  n,  representing  the  number  of  rows  of  rivets,  thus: 

n  a 
p  =  —  +d       .        .        .         .      (5). 

The  different  resisting  power  of  equal  areas  of  section,  as  many  times  found  by  tests  of 
the  shearing  stress  of  the  rivets  and  the  tensile  stress  of  the  plates,  is  not  taken  into  account 
in  the  make-up  of  these  rules.  They  are  treated  in  all  cases  as  equals  under  the  strains  of 
continued  use.  That  is  to  say  —  The  Philadelphia  Boiler  Ordinance  and  the  English  rules 
alike  impliedly  declare  :  The  shearing  strength  of  the  rivets  is  just  equal  to  the  tensional 
strength  of  the  plates  per  square  inch  of  area  in  boilers  made  of  iron  plates  and  iron  rivets. 

If  any  one  takes  exception  to  this  treatment  of  the  two  Strains,  the  formulae  permit 
him  to  introduce  his  own  figures  of  difference  into  their  make-up,  by  which  he  can  get  a 
result  in  accordance  with  his  own  belief  ;  but  of  the  mathematical  base  embodied  in  the 
formulae,  we  are  sure. 

For  single  and  multiple  riveted  joints  when  steel  plates  are  secured  by  iron  or  steel 
rivets,  the  relative  resistance  of  the  plates  to  tension  and  of  the  rivets  to  shear  must  be  in- 
serted in  the  formula.  First,  let  us  assume,  as  the  rules  for  inspection  have  done  and  do  in 
all  cases,  that,  area  for  area  subjected  to  stress  and  acting  together,  iron  plates  and  iron 
rivets  are  equal  in  resistance.  The  best  Staffordshire  iron  boiler  plates  will  stand  48,000 
Ibs.  tension  per  square  inch  of  section  ;  but  the  Board  of  Trade  and  Lloyd's  limit  all  best 
iron  plates  and  rivets  alike  to  47,000  Ibs.  The  Philadelphia  Ordinance  will  pass  iron  plates 
which  have  shown  on  test  a  tension  of  50,000  Ibs.  per  square  inch,  but  will  allow  no  more 
whatever  the  plates  may  show,  and  will  give  full  credit  to  a  joint  in  which  the  driven 
rivets  have  equal  section  to  the  punched  plates.  And  yet  we  well  know  it  to  be  a  matter 
of  fact  that  the  shearing  strength  is  less  than  the  tensile  strength  of  the  same  material. 
Mr.  William  H.  Shock's  experiments  on  American  iron  gave  as  a  mean  for  single  shear 
41.033  Ibs.  per  square  inch,  and  78,030  Ibs.  for  double  shear,  these  experiments  being  made 
upon  iron  bolts  in  a  shearing  device  which  did  not  include  the  uncertain  element  of  friction 
by  the  rough  surfaces  of  the  plates  when  bound  closely  by  the  rivets  of  a  riveted  joint 
made  in  the  usual  way. 

When  iron  rivets  are  used  wTith  steel  plates  they  are  accepted  under  the  rules  for  just 
what  they  are  worth  under  shear  and  no  more.  The  English  rules  say:  "  Iron  rivets  in 
steel  boilers  should  have  a  section  of  -\3-  of  the  plate  section."  Steel  rivets  must  be  calcu- 
lated from  their  actual  strength  to  resist  shearing  ;  and  for  these  the  fraction  |f  will  express 
the  larger  area  they  must  have  to  the  plates  with  which  they  are  used  to  make  joints,  sim- 
ply because  steel  plates  show  an  ultimate  tensile  strength  of  28  tons,  and  steel  rivets  an 
ultimate  shearing  strength  of  23  tons  per  square  inch  of  section.  The  old  rules  published 
by  Fairbairn,  and  used  by  him  and  by  many  boiler-makers  since,  are  obsolete  now,  in  the 
liirht  of  the  later  method  of  proportioning  joints  and  the  laws  which  sanction  their  use, 
although  lie  furnished  the  first  material  for  the  base  upon  which  this  law  has  been  built. 
From  an  extended  list  of  all  iron  single  joints,  proportioned  on  the  principle  of  equality  of 
sectional  areas,  the  percentage  of  joint  strength  to  the  solid  plate  will  reach  to  .64  and  in 
double  joints  to  .78  and  be  practically  tight  under  pressures  up  to  say  100  Ibs.  of  steam  per 
square  inch  — a  material  increase  over  the  oft-quoted  figures  of  .56  and  .70  originated  and 
recommended  by  Fairbairn. 

If  we  accept  the  inspection  laws  referred  to,  assuming  even  results  of  the  two  strains, 
then  rules  4  and  5  will  find  the  proper  pitches  for  boiler  joints  made  of  iron  plates  and  iron 
rivets  ;  but  in  composite  boiler  shells,  the  introduction  of  symbols  representing  the  actual 
powers  of  resistance  of  the  components,  will  be  necessary  :  we  will  then  have  for  double 
or  multiple  joints  ; 


104  THE    LOCOMOTIVE.  [JULY, 


n  a  S 

p  =  —    ._.  +  d      .        .        .        .      (6), 
t  T 

which  can  be  applied  also  to  an  all-iron  joint  or  to  joints  made  of  other  materials  than  the 
usual  iron  and  steel.  If  we  desire  to  tind  the  pitch  of  the  rivets,  when  the  rivet  diameter 
and  a  certain  percentage  of  joint  strength  are  given,  we  may  use  the  following  formula  : 


.      .      .        . 

(100-*) 

This  do^s  not  include  the  thickness  of  the  plates;  it  relates  only  to  the  proportion  existing 
between  the  distance  from  center  to  center  of  the  rivet  holes  and  the  space  between  the 
holes. 

Other  convenient  formulae  are  readily  obtained  from  A,  B,  and  C,  by  transposition  ; 
as,  for  instance,  if  it  is  desired  to  know  the  shear  to  which  the  rivets  are  exposed  in  any  par- 
ticular case  after  all  the  elements  have  been  obtained  —  the  formula  will  take  this  shape  : 

Cx  Rxf 

Shear  =  -  --,        .        .        .      (8), 

tX  B 

and  will  give  the  Ibs.  per  square  inch  of  cross-section  to  which  the  rivets  are  subjected  in 
the  seam  by  the  steam  pressure  C,  which  has  been  obtained  by  the  Ordinance  formula. 

The  rivet  hole  determines  the  size  and  measure  of  the  rivet  after  it  is  driven,  because  it 
is  then  filled  by  it  ;  and  in  making  calculations  with  the  aid  of  these  formulae,  the  trade 
sizes  of  the  rivets  must  not  be  taken.  In  punching  holes  for  rivets  in  boiler  plates,  it  is  the 
usual  practice  to  use  punches  y1^  of  an  inch  greater  in  diameter  than  the  trade  diameter  of 
the  rivets,  and  it  is  also  usual  to  make  the  dies  which  are  used  with  the  punches  ^  of  an 
inch  larger  in  diameter  than  the  punches  to  be  used  with  them.  The  result  of  this  method 
is  to  make  conical  holes  in  the  plates,  corresponding  to  the  sizes  of  punch  and  die.  If  the 
punched  holes  are  net  to  the  dimensions  of  the  'punch  and  die  here  given,  and  if  the 
material  of  the  plate  immediately  around  the  hole  has  not  suffered  in  the  act  of  punching, 
then  the  proper  size  of  holes  to  be  used  in  the  formula  would  be  the  mean  diameter  of  the 
conical  holes  so  made,  instead  of  Ty  larger  than  the  punch,  as  they  are  usually  assumed  to 
be.  It  is  well  known,  however,  that  the  material  of  the  plates  bordering  the  holes  is 
weakened  by  the  detrusion  of  the  punch  ;  to  what  distance  this  reaches  from  the  surface  of 
visible  separation  of  the  metal  may  not  be  definitely  known,  and  must  necessarily  be  differ- 
ent with  different  materials  and  punches  —  but  it  is  certain  to  be  a  small  measurable  dis- 
tance into  the  plate  around  the  hole.  If  we  take  the  diameter  of  the  punched  holes  to  be  equal 
to  that  of  the  die,  we  will  not  be  far  from  the  actual  state  of  the  case,  especially  as  some 
of  this  disturbed  metal  is  removed  by  the  reamer  or  crushed  by  the  drift-pin.  We  are  safe 
in  this  assumption  in  so  far  as  the  ultimate  strength  of  the  joint  is  concerned,  'because,  as 
usually  happens  in  rupture,  the  plates  give  way,  while  the  rivets  rarely  fail  ;  and  again,  the 
plates  suffer  loss  of  substance  by  wear  and  waste,  while  the  rivets  are  preserved  against 
deterioration,  and  therefore  the  initial  strength  of  the  plates  ought  to  be  favored. 

In  view  of  these  facts,  the  suggestion  is  here  made  that  when  we  wish  to  determine 
pitches  from  given  plates  and  rivets,  that  we  use  the  greater  diameter  of  the  punched  hole, 
whatever  that  may  be,  for  the  quantity  expressed  by  a  in  all  of  these  formulas,  and  that  we 
assume  the  rivet  diameter  to  be  that  of  the  lesser  diameter,  or  reamed-out  diameter  of  the 
rivet-hole.  The  result  of  this  apportionment  of  the  material  will  be  effectively  to 
strengthen  the  plates,  which  all  experience  has  proven  to  be  necessary  ;  so  that  while  this. 
decision  appears  to  be  against  reason  and  the  isolated  facts  of  experiment  —  the  resistance 
to  shearing  always  proving,  less  than  that  to  direct  tension  in  the  same  material  —  it  must 
be  constantly  borne  in  mind  that  the  strain  on  the  plates  and  rivets  are  not  direct  in  the 
ordinary  lap-joint  as  they  are  used  in  a  boiler,  the  plates  being  subjected  to  some  transverse 


1889.]  THE    LOCOMOTIVE.  105 

strain  while  under  tension,  and  the  rivets  to  some  tensile  strain  while  under  shear. 
Strictly  speaking,  the  plate  loses  what  is  punched  out  of  it,  together  with  the  metal  de- 
stroyed around  the  punched  hole,  and  the  rivet  gains  by  whatever  increased  diameter  it 
gets  in  the  process  of  riveting.  They  should  be  estimated  upon  what  they  actually  are 
when  the  joint  is  made  up. 


MATERIALS— STRENGTH   OF    THE    STRUCTURE.         11$ 

a  trace  of  fracture.  Such  a  rivet,  split  and  "  etched  "  on  the 
cut  surfaces,  shows  a  smoothly  curved  grain,  uniform  texture 
and  color,  and  no  visible  sign  of  the  presence  of  slag.  Such  a 
rivet,  made  of  good  rivet-steel,  will  show  absolute  uniformity 
of  surface,  and  no  trace  even  of  "  grain." 

The  chemical  composition  of  these  rivet-steels  should  be  as 
nearly  as  possible  that  of  the  best  rivet-irons ;  they  should  con- 
tain the  least  possible  proportion  of  the  hardening  elements, 
including  carbon  and  manganese,  as  well  as  phosphorus,  and 
should  be  so  pure  as  to  readily  take  a  surface  like  that  of  a 
mirror,  when  polished. 

49.  The  Sizes  of  Rivets,  their  form  and  strength,  are 
quite  well  settled  by  experience  and  by  test.  The  rivet  con- 
sists, as  supplied  by  the  market,  of  a  straight  or  slightly  tapered 
body,  circular  in  section,  and  having  a  head  1.5  or  1.6  the  di- 
ameter of  the  shank;  the  latter  is  2  to  3  or  4  per  cent  smaller 
than  the  hole  which  it  is  to  fill,  and  tapers  toward  the  end  to 
a  diameter  about  0.95  that  of  the  hole.  The  head  is  cylindri- 
cal, and  has  a  thickness  0.7  or  0.75  the  diameter  of  the  body  of 
the  rivet.  The  length  of  the  shank  or  body  is  2.25  or  2.50 
times  the  diameter  of  the  hole,  and  the  latter  is  often  equal  to 
the  double  thickness  of  plates  held  together  by  it.  When  in 
place,  the  small  end  is  driven  down  by  hand-hammers  or  by  the 
riveting  machines  to  form  a  cone-shaped  or  hemispherical 
head,  the  sheets  riveted  together  being  thus  confined  by  the 
two  heads  and  sustained  by  the  strength  of  the  shank  against 
any  force  tending  to  separate  them.  The  principal  stresses 
exerted  on  the  rivet  are  usually  shearing.  The  rivets,  when 
heated,  should  be  brought  up  to  a  full,  clear  red  heat.  A 
simple  rule  sometimes  used  to  determine  the  diameter  of  a 
rivets  is  that  of  Unwin,  who  makes  this  diameter 

d—  1.2  V~t, 

in  which  /  is  the  thickness  of  the  single  plate  or  sheet.  The 
following  table  is  thus  obtained,  taking  the  nearest 


THE   STEAM-BOILER. 


Thickness 
of  Plate. 
1 

Diameter,  </, 
of  Rivet. 

•J-   —  o  50 

.   A  —  0.^6 

4 

.  44  —  o  68 

—  O  7*i 

A    . 

.   4-?  -  0.80 

Thickness 
of  Plate. 

»     . 

Diameter,  d, 
of  Rivet. 

1   —  o  86 

4 

T^   —  O  0-1 

f 

I  -,1,  —  I  06 

i 

I-t    —   11^ 

i    , 

.    li    —   1.25 

The  driven  rivet  is  something  like  four  or  five  per  cent 
larger  than  fhe  undriven. 

The  following  table  gives  the  proportions  of  rivets  adopted 
in  some  of  the  best  establishments  in  the  United  States,*  and 
the  relative  strength  of  joint  secured : 

TABLE  OF    THE  PROPORTIONS   OF   RIVETS. 


Thickness  of  plate 

i" 

V 

4" 

^7." 

4." 

Diameter  of  rivet 

| 

11 

£ 

« 

| 

Diameter  o    rivet-hole  
Pitch  —  single-riveting  

H 

2 

1  6 
2A- 

11 

2i 

? 
2A 

H 

2! 

Pitch  —  double-riveting  

3 

!|i 

«li 

•3-1 

^4 

Strength  of  single-riveted  joint.  .  . 
Strength  of  double-riveted  joint.. 

.66 

•77 

.64 
.76 

.62 

•75 

.60 
•74 

•  58 

•73 

Plates  more  than  ^'  thick  should  never  be  joined  with  lap- 
joints.  When  it  is  necessary  to  use  them  a  butt-joint  with  a 
double  fish-plate  should  always  be  used.  In  recommending  the 
above  proportions  we  assume  that  the  workmanship  is  always 
fair. 

The  common  proportions  of  rivets,  as  given  by  Unwin,t  are 
seen  in  the  accompanying  figure ;  that 
illustrated  is  of  such  form  as  will  permit 
the  formation  of  the  conical  head,  the 
total  length  being  about  2\  times  the 
diameter  when  a  double  thickness  of 
plates  is  to  be  secured  together. 

The  next    figures  exhibit   the   differ- 
j.6   trr^^  '    ence  jn  proportions   of  rivets   for  hand- 
[^  riveting  and  for   steam-riveting,  as   given 

FIG.  63.  by  the  same  authority;    the  first  figure 

showing  two  forms  of  head  for  hand-work,  the  second  two  for 


*  Locomotive,  July,  1882. 
f  Machine  Design, 


MATERIALS— STRENGTH  OF    THE    STRUCTURE. 
steam-riveted  work :  one  of   each  pair  is  set  in  a  straight  hole, 


FIG.  64. 


the  other  in  a  chamfered  hole.     The  next  figure  gives  the  pro- 
portions for  a  countersunk  rivet,  used  in  ship-building. 

50.  The  Strength  of  Seams,  when  riveting  is  used,  varies 
with  the  character  of  the  metal,  the  method  of  riveting,  and 
the  quality  of  workmanship.  A  single-riveted  joint  has  usually 
not  far  from  60  per  cent  of  the  strength  of  the  solid  sheet,  a 
double-riveted  seam  70  per  cent ;  and 
the  strength  may  be  still  further  in- 
creased by  adding  to  the  number  of 
rows  of  rivets,  with  proper  distribu- 
tion. The  joint  is  so  proportioned 
that  the  fracture  will  occur  by  shear- 
ing the  rivets  rather  than  by  breaking 
out  the  edge  of  the  sheet  or  tearing 
away  the  lap  bodily.  The  lap  usually 
extends  beyond  the  rivet-hole  about 
1.5  times  the  diameter  of  the  rivet. 

To  secure  maximum  "  efficiency"  of  seam,  i.e.,  equal  and 
maximum  resistance  in  all  directions  of  possible  stress,  it  is 
evident  that  the  joint  must  be  equally  liable  to  tear  along  the 
line  of  rivets,  to  shear  the  rivets,  and  to  tear  them  out  by  pull- 
ing them  through  the  lap.  For  a  single-riveted  joint  there- 
fore, if  F  represent  the  tearing  force,  T  the  tenacity  of  the 
sheet,  SS'  the  shearing  resistance  of  the  rivet  and  sheet,  C  its 
resistance  to  crushing,/  the  "pitch,"  and  d  the  diameter  of  the 


FIG.  66. 


THE   STEAM-BOILER. 


rivets,  /  the  width  of  lap,  and  /  the  thickness  of  the  sheet,  we 
must  have 


=  \7td*S'  =  Cdt  =  (p-  d}Tt  = 


or,  if  the  lap  is  made  over  strong,  as  above,  and  if  crushing  is 
not  anticipated,  both  of  which  are  usual  conditions, 


and 

_  \7td*S+dtT  _  i  nd*S 
P'-  ~Tt~         ~4~7T~ 

Where,  as  sometimes  is  the  case,  the  joint  is  a  butt-joint 
and  the  rivets  are  thus  "  in  double  shear," 


and  the  same  expression  serves  for  the  case  of  double-riveted 
seams  made,  as  with  single-riveting,  with  a  lap,  but  having  a 
second  line  of  rivets  behind  and  reinforcing  the  first. 

Where  the  rivet  and  the  plate  are  of  the  same  material,  or 
wherever  the  resistance  to  shearing  and  the  tenacity  may  be 
taken  as  substantially  equal,  the  formula 


may  be  adopted,  in  which  /,  d,  n,  and  t  are,  respectively,  the 
pitch  of  rivets,  centre  to  centre,  the  diameter  of  rivet,  the 
number  of  parallel  rows,  and  the  thickness  of  sheet. 

The  following  tables  represent  proportions  for  adoption  in 
designing,  the  ratio  of  T  to  C  being  taken  for  iron  and  steel  of 
various  qualities,  as  assumed  by  Unwin:* 


*  See  Machine  Design,  by  W.  C.  Unvvin.     London  :  Longmans,  Green  &  Co. 


MATERIALS—  STRENGTH   OF    THE    STRUCTURE. 


SINGLE-RIVETING. 


IKON  RIVETS  AND  PLATES. 

STEEL  RIVETS  AND  PLATES. 

; 

^IN  INCHES. 

Punched 
Plates. 

Plates 
Drilled. 

Plates 
Punched. 

Plates  Drilled 
or  Punched 
and  Annealed. 

Nomi- 
nal. 

Actual. 

Pitch/  for  values  of  —  = 

0.75 

0.85 

0.95 

I.O 

1.05 

I.I5 

1.25 

1-35 

t 

H 

0.72 
0.78 

2.45 

2-5 

2.25 
2-3 

2.1 
2.  1 

2.0 
2.1 

2.0 
2.O 

1.85 
1.9 

1.8 
1.8 

•7 

-7 

TV 

it 

0.85 

2.6 

2.4 

2.2 

2.15 

2.1 

2.O 

1.9 

.8 

i 

i 

0.92 

2-7 

2-5 

2-3 

2.2 

2.1 

2.1 

2.O 

•9 

i 

H 

0.98 

2.6 

2.4 

2-3 

2.2 

2.1 

2.O 

2.0 

•9 

* 

iyV 

I  .  IO 

2.8 

2.6 

2.4 

2.4 

2-3 

2.2 

2.  I 

2.0 

i 

If 

1.17 

2.9 

2.7 

2.5 

2-5 

2.4 

2.25 

2.2 

2.15 

i 

I* 

1.30 

3-1 

2.9 

2.7 

2.6 

2.6 

2-45 

2.4 

2-3 

DOUBLE-RIVETING. 


IRON  RIVETS.—  PLATES 

STEEL  RIVETS.  —  PLATES 

d  IN  INCHES. 

Punched. 

Drilled. 

Punched. 

Drilled. 

Nomi- 

Actual. 

Pitch  of  rivets  for  value  of  —  = 

nal. 

0.85 

1.  00 

1.  10 

1.20 

1-35 

h 

H 

0.72 

3.8 

3-3 

3-1 

2.9 

2.7 

! 

*  - 

0.78 

3-8 

3-4 

3-1 

2.9 

2.7 

1 

3 

0.85 
0.92 

3-9 
4.0 

3-5 
3-6 

3-2 
3-4 

3-0 
3-2 

2.8 

2.9 

i 

H 

0.98 

3-9 

3-4 

3-2 

3-0 

2.8 

i 

*S 

I.  IO 

4.0 

3-6 

3-4 

3-2 

3.0 

i 

i| 

1.  17 

4.1 

3-7 

3-5 

3-3 

3.1 

i 

i± 

1.30 

4-4 

3-9 

3-7 

3-5 

3.3 

Joints  proportioned  as  above  range,  in  their '"  efficiencies," 
from  40  to  60  per  cent  in  the  single-riveted  seams,  and  from 
60  to  80  per  cent  for  double-riveting;  the  smallest  rivets  and 
thinnest  plates  giving  the  smallest,  and  the  larger  work  the 
largest,  values.  The  average  efficiencies  may  be  taken  as 
follows: 

Single-riveting  : 

Size  of  rivet ,  T\     f      &     £      f      £      |       I 

Efficiency 55     55     53     52     48     47     45     43 

Double -rive  ting  • 

Efficiency 75     73     72     71     67     66     64     63 


I2O  THE   STEAM-BOILER. 

The  strength  of  a  seam  is  obtained  by  multiplying  the 
resistance  of  the  solid  sheet  by  the  efficiency  of  the  joint. 

The  strength  of  well-made  joints,  as  exhibited  by  test,  in 
proportion  to  strength  of  the  original  plate,  according  to  Clarke, 
are  for  plates  -f-inch  thick  and  less,  for  the  best  English  York- 
shire iron: 

Working  Strength. 

Original  strength  of  plate 100  11,000  Ibs.  per  sq.  inch. 

Single-riveted  lap-joint 60  6,700        "  " 

Double-riveted  lap-joint 72  8,000        "  " 

Double-riveted  butt-joint 80  9,000        "  " 

Fairbairn  found  the  strength  of  joints  to  be  as  follows: 

Strength  of  plate 100  Bursting  tension .   34,000  Ibs. 

Double-riveted  joint 70  Proof  tension   ...   17,000    " 

Single  riveted  joint 56  Working  tension.     4,250   " 

the  working  tension  being  taken  as  •§•  of  the  bursting  tension. 
For  cast-iron  pipes  the  working  tension  may  be  estimated  at  -J- 
the  bursting  pressure,  and  at  about 

16,500  Ibs.  per  sq.  inch  for  bursting  tension, 
5,500    "          "         "       "    proof  tension, 
2,750    ''         "         "      "   working  tension. 

Welded  joints  for  boilers  have,  if  perfect,  the  same  strength 
as  the  original  plate,  but  they  are  apt  to  be  uncertain. 

The  thickness  of  plates  is  limited  for  best  work.  Very  thin 
plates  cannot  be  well  calked,  and  thick  plates  cannot  be  safely 
riveted.  The  limits  are  about  \  of  an  inch  for  the  lower  limit, 
and  f  of  an  inch  for  the  higher  limit.  The  riveting  machine 
only  can  be  used  for  very  thick  plates,  a  thickness  of  half  an 
inch  being  about  the  limit  of  hand-riveting. 

In  some  cases  the  seams  of  the  shells  or  the  flues  of  boilers 
are  put  together  in  helical  form,  and  some  increase  of  strength 
is  thus  secured  in  the  longitudinal  at  the  expense  of  the  girth- 
seams.  If  n  represent  the  ratio  of  the  projected  length  of  the 
seam  on  the  circumference  to  the  corresponding  length  of  the 


MATERIALS— STRENGTH  OF    THE   STRUCTURE. 


121 


projection  longitudinally,  the  ratio  of  strength,  as   compared 
with  the  common  seam,  is  measured  by  the  ratio 


m  — 


For,  in  Fig.  67,  let  ABC  represent  a  part  of  a  sheet 
on  which  the  diagonal  AC  is  the  line  of  the  joint; 
AB  is  the  corresponding  longitudinal  joint,  as  com- 
monly made,  and  BC  the  girth  seam. 

Then  the  stress  per  unit  of  length 
of  AB  will  be  unity  ;  that  on  BC  will 
\  be  2,  and  the  total  stresses  will  be, 
respectively,  2  and  n,  where  n  meas- 
ures the  ratio  of  BC  to  AB,  or  the 
"  rake"  of  the  seam.  The  total  re- 
sultant stress  will  be  BE  on  the  joint 
AC,  and  its  normal  component  will 
be  BE,  the  sum  of  the  components 
of  those  on  the  longitudinal  and 
girth  seams,  AB  and  BC,  resolved 
perpendicular  to  AC,  and  the  in- 
tensity  of  that  stress  is  the  quotient 
of  this  sum  divided  by  the  length,  AC,  of  the  seam.  Hence 
the  intensity  on  AB  will  be 


FIG.  67. 


AB 


_ 

~2; 


that  on  BC  will  be 


nAB 


that  on  A  C  will  be 


*.= 


2  sin  8  --  n  cos  0 


122  THE   STEAM-BOILER. 

But 

sin  6  =  — 7 ;    cos  6  =  — : — 


and 

_?l±i       A    **-    n*  +  2       r 
'3  -  -  - 


When  n  is  given  the  values  below,  the  ratios  of  strength  of 
seam  are  as  tabulated. 

STRENGTH  OF  HELICAL  SEAM. 
(Common  longitudinal  seam  =  i.) 


n  m 

o  .  i.o 


1.4 
1-5 


n  m 

1-75  .................   1.6 

2.00  .................   1.7. 

3.00  .................   1.8 

«>  ..........  .    2.0 


When  n  =  o  the  joint  is  parallel  with  the  axis  of  the  cylin- 
der; it  becomes  a  longitudinal  seam.  When  n  •=.  oo  ,  it  becomes 
a  girth-seam  of  twice  the  relative  strength.  When  the  angle  of 
"rake"  is  30°,  the  gain  is  10  per  cent;  when  45°,  the  gain  be- 
comes 0.4.  It  is  obvious  that  this  form  of  seam  is  very  waste- 
ful of  metal,  if  so  much  inclined  as  to  secure  any  considerable 
gain  of  strength,  if  the  boiler  or  the  flue  is  built  of  a  succession 
of  ring  courses  laid  side  by  side ;  in  such  constructions  as  Root's 
"  spiral  pipe,"  in  which  the  courses  are  helical,  this  objection 
does  not  hold. 

The  "  factor  of  safety,"  as  stated  where  reference  is  made  to 
the  strength  of  steam-boilers,  is  usually  misleading,  as,  for  ex- 
ample, in  the  U.  S.  regulations.  Pressures  one  sixth  those 
computed  from  the  reports  of  tests  of  strength  of  the  plate  are 
permitted ;  but  the  real  factor  of  safety  is  obtained  by  multi- 
plying this  nominal  factor  by  the  coefficient  of  strength  of  seam. 
Thus,  where  the  lawr  allows  six  the  real  factor  is  0.56  X  6  —  3.36 


MATERIALS— STRENGTH   OF   THE   STRUCTURE.         123 

for  the  single-riveted  seam,  or  0.7  X  6  =  4.2  for  double-riveting, 
Fairbairn's  coefficients  being  accepted.  The  real  factor  should 
not  be  less  than  six,  and  some  authorities,  following  Rankine, 
would  make  it  eight,  and  others  even  ten. 

51.  Punched  and  Drilled  Plates  usually  differ  in  strength, 
but  each  may  be  either  stronger  or  weaker  than  unperforated 
metal  of  equal  area  of  fractured  section.  When  the  metal  is 
very  soft  and  ductile,  the  operation  of  punching  does  no  appre- 
ciable injury,  and  the  Author  has  sometimes  found  it  actually 
productive  of  increased  strength,  the  flow  of  particles  from  the 
hole  into  the  surrounding  parts  causing  stiffening  and  strength- 
ening. With  most  steel  and  with  hard  iron  the  effect  of 
punching  is  often  to  produce  serious  weakening  and  a  tendency 
to  crack,  which  has  in  some  cases  resulted  seriously.  With 
metal  of  the  first  class,  punching  is  perfectly  allowable ;  with 
iron  or  steel  of  the  second  class,  drilling  should  always  be  prac- 
tised. It  is  customary,  in  the  practice  of  the  most  reputable 
engineers  and  builders,  to  drill  all  steel  plates,  but  usually  to 
punch  iron.  Sometimes  the  steel  plate  is  punched  with  a 
punch  of  smaller  diameter  than  the  proposed  rivet,  and  is  sub- 
sequently reamed  out  or  counterbored  to  size.  It  is  generally 
assumed  that  this  method  is  perfectly  safe. 

Messrs.  Greig  and  Eyth,  after  a  long  and  carefully  con- 
ducted investigation,  say:* 

"  The  experiments  show  that  the  plates  invariably  lose  part 
of  their  tensile  strength  in  the  section  of  solid  material  left 
between  the  rivets  of  a  seam,  this  loss  being  greatest  in  lap- 
joints.  It  is  also  greater  in  punched  than  in  drilled  plates 
(iron  as  well  as  steel),  and  greater  in  plates  riveted  together  by 
steam,  than  in  those  riveted  by  hydraulic  pressure.  On  the 
other  hand,  the  strength  of  rivets  against  shearing  is  greater 
than  its  normal  figure,  especially  in  lap-joints. 

"  The  usefulness  of  double-riveting  appears  to  be  mainly 
due  to  the  fact  that  it  more  effectually  prevents  lap-jointed 
plates  from  bending  under  stress.  At  the  same  time  the  zig- 
zag riveting  generally  adopted,  in  double-riveting,  increases 

*  Lond.  Engineering,  June  29,  1879. 


124  THE   STEAM-BOILER. 

the  tensile  resistance  of  the  material  between  the  rivets  con- 
siderably beyond  its  normal  figure. 

"  Butt-joints,  with  a  cover  on  one  side  of  the  plate  only, 
gave  no  advantage  at  all,  the  cover  behaving  simply  as  an 
intermediate  plate  attached  to  the  two  main  pieces  by  an  ordi- 
nary lap-joint.  A  marked  improvement  could,  no  doubt,  be 
obtained  by  giving  the  cover  greater  thickness,  so  as  to  prevent 
its  bending. 

"The  most  effective  seams,  as  to  tensile  strength,  were 
butt-joints  with  two  covers,  as  not  only  do  they  nearly  double 
the  shearing  strength  of  each  rivet,  but  they  entirely  prevent 
the  bending  of  the  main  plates.  The  main  fact  resulting  from 
the  tests  of  parts  of  boilers  and  complete  boilers  under  hy- 
draulic pressure  was  the  impossibility  of  bursting  an  ordinary 
rivet-seam  in  this  way,  the  compression  of  the  rivet  and  the 
elongation  of  the  rivet-hole  resulting  invariably  in  leakage, 
which  prevented  the  necessary  pressure  from  being  obtained. 
Each  rivet  becomes  its  own  safety-valve,  and  the  strain  put  on 
the  weakest  part  of  the  structure  never  reached  more  than  70 
per  cent  of  the  breaking  strain.  This  is  the  point  where  addi- 
tional hardness  of  the  material  would  be  most  useful,  as  it 
would  prevent  the  opening  of  the  rivet-holes,  which  now  makes 
a  boiler  useless  long  before  the  breaking  strain  is  reached."  * 

Good  steel  is  much  more  enduring  than  any  iron,  both 
against  ordinary  wear  and  extraordinary  strain. 

The  results  of  experiments  on  the  best  British  steel  for 
ship-building  and  for  boilers,  as  reported  to  Lloyds,  show  that 
the  injury  done  by  punching  is  less  as  the  plates  are  thinner, 
amounting,  in  the  cases  reported,  to  less  than  10  per  cent  in 
sheets  J  inch  (0.6  cm.)  thick,  and  rapidly  increasing,  becoming 
20  per  cent  at  f  inch  (i  cm.),  and  is  still  more  serious  with  the 
heavy  plate  used  for  large  ships  and  for  boilers.  But  the  injury 
was  discovered  to  be  local,  and  confined  to  a  shell  lining  the 
punched  hole,  and  but  about  one  eighth  of  an  inch  (0.3  cm.)  in 
thickness.  This  can  be  readily  cut  out,  and  the  punched  and 
counterbored,  or  reamed,  holes  produce  no  observable  weak- 

*  Lond.  Engineering,  1879. 


MATERIALS— STRENGTH  OF   THE   STRUCTURE.         125 

ness.  In  many  instances  no  special  precautions  are  taken  in 
this  direction  where  the  metal  is  less  than  one  half  inch  (1.25 
cm.)  in  thickness. 

52.  Hand-riveting  and  Steam-riveting  are  both  prac- 
tised by  good  makers,  and  authorities  are  somewhat  divided  in 
opinion  as  to  their  relative  merit.  With  either  system,  good 
work  may  be  done  by  a  good  workman ;  by  either  method, 
dangerously  defective  boilers  may  be  produced.  With  a  prop- 
erly designed  riveting  machine  of  the  right  size  for  its  work, 
and  carefully  manipulated,  very  perfect  work  may  be  done. 
Careless  handling  produces  distorted  rivets,  eccentrically  placed 
heads,  and  sometimes  causes  the  formation  of  a  "  fin"  on  the 
rivet,  which,  entering  between  the  sheets  to  be  riveted  to- 
gether, holds  them  apart  and  causes  leakage  along  the  seam. 
When  the  plates  are  well  adjusted,  in  metallic  contact,  and  per- 
fectly secured,  before  the  rivet  is  "  headed  up,"  this  last  defect 
is  not  likely  to  appear.  The  careful  adjustment  of  the  rivet- 
head  to  the  die  which  supports  it  against  the  blow  of  the  ma- 
chine, and  the  exact  alignment  of  rivet  and  striking  die,  will 
prevent  distortion  of  the  rivet  by  the  blow.  Sometimes  the 
machine  is  too  light  for  its  work ;  in  such  cases  two  blows  may 
be  necessary  to  completely  form  the  head  and  to  expand  the 
body  of  the  rivet  sufficiently  to  fill  the  rivet-hole. 

In  hand-riveting  the  action  of  the  hammer  often  hardens 
the  metal  in  the  head,  and  gives  it  such  rigidity  and  brittleness 
that  it  may  even  fly  off  at  the  last  stroke  of  the  riveting  ham- 
mer. The  cone-shaped  head  is  a  comparatively  weak  form,  and 
it  is  better  to  use  a  cup-shaped  die,  or  former,  and  a  larger 
hammer  striking  fewer  and  heavier  blows,  to  form  a  hemi- 
spherical head,  which  latter  is  much  stronger,  and  neater  in 
appearance.  Work  of  this  kind  may  be  quite  as  good  as  the 
best  machine-riveting,  but  it  is  usually — not  invariably — more 
costly. 

Riveting  machines  constructed  with  two  dies  moved  inde- 
pendently— the  one  a  hollow  die,  having  for  its  office  the  closing 
up  of  the  lap  simply;  the  other  a  solid  die,  which  immediately 
follows  up  the  first  and  sets  up  the  rivet — are  probably  much 
better  than  the  more  common  form  of  riveter  having  one  die 


126  THE   STEAM-BOILER, 

only.     Messrs.  Greig  and  Eyth  found  the  following  to  be  the 
pressures  attained  on  the  heads  of  f-inch  steel  rivets  :* 

Lbs. 

Steam- riveter 82,380 

Hydraulic  stationary 86,360 

Hydraulic  portable 44,018 

Power  light  blow 69,384 

Power  heavy  blow 115,640 

The  best  work  was  done  by  the  steam-riveter. 
They  conclude  that — 

"  The  well-known  fact  of  the  superiority  of  riveting  by 
machinery  over  hand-riveting  has  been  again  demonstrated 
most  conclusively,  while  the  experiments  have  shown  that  the 
effects  of  steam-riveting  is,  to  say  the  least  of  it,  not  inferior 
to  hydraulic  riveting  as  far  as  the  quality  of  the  rivet  is  con- 
cerned, but  that  the  hydraulic  riveting  is  distinctly  superior  as 
to  its  effects  on  the  plate,  which  is  less  injured  by  the  slow 
pressure  of  the  hydraulic  ram. 

"  Steel  showed  in  this  respect  a  decided  superiority  over 
iron  beyond  the  proportion  due  to  its  greater  tensile  and  shear- 
ing strength." 

The  conclusions  of  Mr.  J.  M.  Allen  are  that  machine-rivet- 
ing probably  results  in  a  greater  proportion  of  defective  rivets 
than  any  other  one  cause.  Machine-riveting  to  make  good 
work  must  be  very  carefully  done.  The  rivet-hole  must  be  truly 
in  line  with  the  machine  dies.  The  holes  in  the  two  plates 
must  also  be  in  line  with  each  other.  If  there  is  an  offset 
between  them,  the  rivet  is  sure  to  be  a  very  bad  one.  The 
most  satisfactory  riveting  of  boiler-plates  is  done  by  a  prop- 
erly constructed  and  used  button-set.  By  this  means  better 
and  more  rapid  work  can  be  done  than  by  hand-riveting.  A 
well-constructed  machine  will  work  quicker  than  the  set,  but 
we  have  rarely  seen  a  complete  job  of  machine-riveting  which 
left  nothing  to  be  desired.  It  was  not  the  fault  of  the  machine, 
however.  In  hand-riveting  the  excellence  of  the  joint  depends 

*  Lond.  Engineering,  June  29,  1879. 


MATERIALS— STRENGTH   OF   THE   STRUCTURE. 

upon  the  form  of  the  set.  With  an  improper  set  it  is  impos- 
sible to  do  good  work,  no  matter  how  skilful  the  workmen 
may  be. 

53.  Welded    Seams   are    considered   better   than   riveted, 
where  facilities  for  welding  are  provided  such  that  the  weld 
may  be   made  with  certainty  and  invariably  perfect.     Unless 
special  and  very  complete  arrangements  are  made  for  securing 
absolute  metallic  contact,  a  good  welding  heat  without  oxida- 
tion, and  thorough  union  by  pressure  or  impact,  welds  are  very 
apt  to  prove  exceedingly  unreliable.     A  gas-furnace,  with  a  de- 
oxidizing flame  of  large  volume  and  covering  a  considerable 
length   of  seam,  has  done  good  work,  and  some  makers  are 
adopting  this  system  to  the  exclusion  of  riveting.     Large  boilers 
are  sometimes  made  without  the  use  of  a  single  rivet  in  any 
important  line  of  junction.     It  seems  possible,  and   even  prob- 
able, that  welding  may  in  time    displace  riveting  in  all  good 
boiler  construction. 

54.  "  Struck-up"  or  Pressed  Shapes  are  adopted,  in  pref- 
erence to  riveted  or  even  welded  parts,  wherever  the  form  and 
size  of  the  piece  will  admit.     Dome-tops,  manhole  and  hand- 
hole  plates,  and  sometimes  large  tube  or  flue  sheets,  are  thus 
made.     The  piece  is  made  by  compressing  the  sheet  of  which 
it  is  to  be  constructed  between  a  pair  of  dies,  and  thus  compel- 
ling it  to  take  the  shape  of  the  intermediate  space,  which  is  that 
of  the  finished   piece.     The  pressure  is  commonly  applied  by 
means  of  the  hydraulic   press.     Small  pieces  are  shaped  in  the 
drop-press,  or  drop-hammer,  in  which  the  dies  are   forced   to- 
gether by  the  blow  of  a  heavy  "  tup,"  or  hammer,  falling  from 
a  height  of  from  two  to  six  feet  or  more,  according  to  the  size 
and  the  intricacy  of  form  of  the  part  to  be  produced. 

55.  Cast  and  Malleableized  Iron,  Brass,  and  Copper  all 
have  limited  application  in  steam-boilers. 

Cast-iron  is  used  in  the  construction  of  manhole  plates,  of 
some  of  the  fittings,  and  even,  in  many  instances,  in  the  heads 
of  plain  cylindrical  and  flue  boilers.  Its  use  is,  however,  always 
to  be  deprecated  where  wrought-iron  can  be  substituted.  When 
it  is  adopted,  in  places  in  which  it  may  be  subjected  to  heavy 
loading,  and  where  its  failure  may  prove  a  serious  matter, 


128  THE   STEAM-BOILER. 

great  care  should  be  taken  to  secure  the  best  possible  quality. 
It  would  be  advisable,  probably,  in  such  cases,  to  use  "  gun- 
iron,"  as  it  is  called,  which  is  cast-iron  of  the  best  grades,  melted 
in  an  "  air-furnace" — a  reverberatory  furnace — and  refined  by 
"  poling,"  or  stirring  with  a  pole,  usually  a  birch  sapling,  until 
its  quality  and  composition  are  satisfactory.  No  contact  being 
allowed  with  the  fuel  or  any  flux  or  other  source  of  contami- 
nation by  phosphorus  or  other  objectionable  element,  greater 
strength  and  toughness  can  be  obtained  than  when  the  melting 
is  done  in  a  "  cupola"  furnace,  in  which  the  iron,  fuel,  and  any 
flux  that  may  be  used  are  mixed  together.  The  process  is  ex 
pensive ;  but  the  product  is  correspondingly  valuable,  the  tena- 
city of  good  gun-iron  exceeding,  often,  30,000  pounds  per  square 
inch  (2109  kgs.  per  sq.  cm.),  and  its  elasticity  and  elastic  resili- 
ence approximating  similar  properties  in  wrought-iron. 

Malleableized  cast-iron  is  usually  given  application  in  small 
castings  forming  parts  of  the  various  attachments  to  boilers. 
It  is  made  by  selecting  a  free-flowing  cast-iron,  as  light  in  grade 
as  possible,  making  the  castings  in  the  usual  way  and  then  sub- 
jecting them  to  a  process  of  prolonged  annealing  at  a  red  heat 
in  the  presence  of  substances  capable  of  abstracting  the  carbon, 
such  as  iron-ore,  blacksmith's  scale,  or  other  materials  rich  in 
oxygen.  The  abstraction  of  the  carbon  thus  leaves  the  casting 
stronger,  somewhat  ductile  and  malleable,  and,  as  a  rule,  a  much 
safer  material  than  when  in  its  original  state ;  it  has  become  a 
crude  wrought-iron.  Only  small  pieces  can  be  successfully 
made  in  this  manner,  except  by  annealing  for  days,  or  even 
several  weeks ;  the  larger  the  casting  the  longer  the  time  de- 
manded. Some  so-called  "  steel-castings"  are  thus  made. 

Brass  and  bronze  are  used  mainly  in  the  encasing  of  pres- 
sure-gauges, water-gauges,  and  similar  appurtenances,  in  the 
construction  of  gauge  and  other  cocks,  and  in  valves  and  their 
seats ;  it  is  less  liable  to  be  cut  away  by  steam,  or  by  water, 
and  hence  brass  valves  keep  tight  longer  than  do  iron  valves  or 
cocks.  Bronze  is  better  than  brass,  but  its  higher  cost  precludes 
its  general  use.  Muntz  metal,  which  consists  of  copper  60,  zinc 
40,  and  gun-bronze,  90  copper  and  10  tin,  are  the  most  generally 
useful  compositions ;  but  the  brasses  in  common  use  generally 


MATERIALS—  STRENGTH  OF   THE   STRUCTURE.         1  29 

contain  more  or  less  of  lead,  and  the  bronzes  are  often  also 
similarly  adulterated.  For  surfaces  exposed  to  friction  the 
addition  of  lead  is  thought  by  many  to  be  an  advantage.  The 
strongest  of  all  such  alloys  is  that  consisting  of  copper  43,  zinc 
55,  and  tin  2,  or  one  having  a  somewhat  less  proportion  of  tin  ; 
this  has  been  called  by  the  Author,  its  discoverer,*  "  maximum 
bronze."  The  presence  of  zinc  or  other  foreign  element  in  the 
real  bronzes  is  found  to  be  particularly  objectionable  in  those 
alloys  intended  for  use  in  salt  water,  as  it  renders  the  latter 
especially  liable  to  injury  by  local  and  rapid  corrosion. 

56.  The  Strength  of  the  Shells  and  Flues  of  boilers  may 
be  readily  calculated  when  the  data  can  be  safely  relied  upon. 
The  two  forms  are  subject  to  quite  different  laws,  however  ;  and 
even  the  strength  of  cylinders  subjected  to  internal  pressure,  as 
are  the  cylindrical  shells  of  steam-boilers,  when  thick,  is  calcu- 
lated by  different  methods  from  those  applicable  when  of  thin 
plate;  but  it  is  not  asserted  that  the  heavy  shells  of  large 
marine  boilers,  in  which  the  metal  is  from  three  quarters  tor 
sometimes,  above  an  inch  thick,  may  not  be  properly  calculated 
by  the  rule  applying  to  thick  cylinders  of  cast-iron  or  other 
non-ductile  material. 

Cylindrical  Boiler-Shells,  and  other  thin  cylinders,  have  a 
thickness  which  is  determined  by  the  tenacity  of  the  metal  and 
the  character  of  the  riveted  or  other  seam.  If/  be  the  internal 
pressure,  T  the  mean  tenacity  to  be  calculated  upon  along  the 
weakest  seam,  r  the  semidiameter,  and  t  the  thickness,  we  have 
for  axial  stresses  for  equilibrium, 

pTtr*  =  27trtT, 
and 


But  for  transverse  stresses  tending  to  rupture  longitudinal 
seams, 

pr  =  tT, 

*  See  "  Materials  of  Engineering:"  The  Alloys- 


I3O  THE   STEAM-BOILER. 

and 

tT  pr 

/  —  — ;     *=^.      ......     (2) 

T  J. 

With  seams  of  equal  strength  in  both  directions,  therefore, 
the  cylinder  is  at  the  point  of  rupture  along  the  longitudinal 
seams,  while  capable  of  bearing  twice  the  pressure  on  girth 
seams.  It  is  evident  that  spheres  have  twice  the  strength  of 
cylinders  of  equal  diameter. 

Tldck  cylinders  are  considered  later,  as  they  are  usually 
made  in  cast-iron. 

Flat  Boiler-heads  are  made  both  in  wrought  and  cast  iron. 
For  these  Clark's  rules  may  be  used.* 

For  elastic  deflection, 

_  ^t 

For  maximum  pressure, 


tT 
p  =  0.2 1 5--, (4) 


or,  for  iron, 
For  steel, 
For  cast-iron, 


/=  10,0007 u    (5) 


p=  11,500-} (6) 


p  =  4,000,  ........    (7) 


when  t  is  the  thickness,  dl  the  diameter,  both  in  inches,  /  the 
pressure  and  T  the  tenacity,  both  in  pounds  per  square  inch. 

*  Inst.  C.  E.,  vol.  liii.,  Abstracts.      London,  1877-78. 


MATERIALS— STRENGTH  OF   THE   STRUCTURE. 
For  spherical  ends, 


where  a  is  108,000   for  wrought-iron,  125,000  for  steel,  45,000 
for  cast-iron,  and  v  is  the  versed  sine  or  rise  of  the  head. 
Lloyd's  Rule  for  cylindrical  shells  of  boilers  is 

abt 

*  =  ->  •  •  •'  -  -  •;-••  (9) 


in  which  a  is  a  constant,  155  to  200  for  iron  and  200  to  260  for 
steel,  b  the  percentage  of  strength  of  solid  sheet  retained  at  the 
joint,  /  is  the  thickness  of  the  plate,  and  d  the  diameter  of  the 
shell.  The  value  of  b  is  thus  reckoned  (n  =  number  of  rows  of 
rivets)  : 


b  =  iocA— — -1,  for  the  plate; 

b  =  100— -1,  for  rivets  in  punched  holes ; 

b  =    90 — -,  for  rivets  in  drilled  holes. 


The  least  of  these  values  is  taken.  Here/,  is  the  pitch  of  rivets, 
dl  is  their  diameter,  al  is  the  area  of  the  rivet-section.  When 
in  double-shear,  1. 75#j  is  taken  for  at.  The  factor  of  safety  is 
taken  at  6,  and  boilers  are  tested  by  water-pressure  up  to  2p. 

The  iron  is  expected  to  have  a  tenacity  of  at  least  21  tons 
per  square  inch ;  steel  must  bear  26  tons  (3307  to  4095  kilogs. 
per  sq.  cm.). 

Welds  are  found,  when  well  made,  to  carry  75  to  85  per 
cent  of  the  strength  of  the  sheet. 

Steam-pife   is   usually  made  with  an  enormous   excess   of 


132  THE   STEAM-BOILER. 

strength  to  meet  accidental  stresses,  such  as  those  due  to 
motion  of  water  within  them.  The  Author  has  tested  pipes 
broken  by  "  water-hammer,"  as  the  engineer  calls  it,  to  1000 
pounds  per  square  inch  (70  kilogrammes  per  sq.  cm.)  after  it 
had  been  thus  cracked  in  regular  work  in  a  long  line,  while 
the  steam-pressure  was  less  than  100  pounds  (7  kilogs.  per  sq. 
cm.).  They  had  all  been  previously  tested  to  about  one  third 
this  pressure. 

Cylinders  of  cast-iron,  for  steam-generators  or  for  steam- 
engines,  are  usually  given  a  thickness  greatly  in  excess  of  that 
demanded  to  safely  resist  the  steam-pressure  ;  often,  according 
to  Haswell, 


for  vertical  cylinders,  where  d  is  the  internal  diameter,  and 

4 (») 


for  horizontal  cylinders  of  considerable  size. 

In  metric   measures,    kilogrammes   and   centimetres,  these 
formulas  become 


If  rl  is  the  external  and  r^  the  internal  radius,  T  the  tena- 
city of  the  metal,  t  its  thickness,  and  /  the  intensity  of  the  in- 
ternal pressure,  we  have,  for  the  thin  cylinder,  as  an  equation 
for  equilibrium, 

pr*  =  T(r,  —  r,)  =  TV,  nearly,   .     .     .     .     (14) 


MATERIALS—  STRENGTH  OF   THE    STRUCTURE.         133 

and 

'-          ...........    OS 


(16) 


For  the  M/f£  cylinder,  however,  the  resistance  at  any  inter- 
nal annulus  of  the  cylinder  is  less  than  T. 

Thick  Cylinders,  technically  so  called,  are  those  which  are 
of  such  thickness  that  the  mean  resistance  falls  considerably 
below  the  full  tenacity  of  the  metal,  as  exhibited  in  thin  cylin- 
ders, in  low-pressure  steam-boiler  shells,  for  example.  Such 
cylinders  are  seen  in  the  "  hydraulic"  press,  and  in  ordnance. 

Barlow*  assumes  the  area  of  section  unchanged  by  stress, 
although  the  annulus  is  thinned  somewhat  by  linear  extension. 
If  this  is  the  fact,  as  the  tension  on  any  elementary  ring  must 
vary  as  the  extension  of  the  ring  within  the  elastic  limit,  the 
stress  in  such  element  will  be  proportional  to  the  reciprocal  of 
the  square  of  its  radius,  i.e.,  it  will  be 


p«>     ;  -    -    v  .   ,    .    .    -    (18) 


and,  taking  the  total  resistance  as/V,,  when  pf  is  the  internal 
fluid  pressure,  since  the  maximum  stress  at  the  inner  radius  is 
T,  that  on  'the  inner  elementary  annulus  is  Tdx,  and  on  any 

other  annulus  —  ^  dx  ;  while  the   total   resistance   will   be,  on 

Ji- 

either  side  the  cylinder, 

*  =  7--f-L  =  T--     (.9) 

* 


Strength  of  Materials,  1867,  p.  118. 


134  THE   STEAM-BOILER. 

The  maximum  stress  is  at  the  interior,  and  may  be  equal, 
as  taken  above,  to  the  tenacity,  T,  of  the  metal ;  then 


and  the  thickness 

;j5  •'••••        t  =  -T=jt> (2I> 

while  the  ratio  of  the  radii 

;:;:;.:        \=Ti^^^  =  T^p;    •   •   -   <»> 

Lame's  Formula,  which  is  more  generally  accepted,  and 
which  is  adopted  by  Rankine,  gives  smaller  and  more  exact 
values  than  that  of  Barlow.  In  the  above,  no  allowance  is  made 
for  the  compressive  action  of  the  internal  expanding  force  upon 
the  metal  of  the  ring.  The  effect  of  the  latter  action  is  to 
make  the  intensity  of  pressure  at  any  ring  less  than  before  by 
a  constant  quantity, 

a 
p  oo  — 2  —  by 

and  the  tension  by  which  the  ring  resists  that  pressure  greater, 


When  r—rvp  =  v,  when  r  —  rv  p  =  pl ; 


then  /,  =  — 2  —  b,     and     o  =  — : ,  —  b ; 

" 


a  =  A 


MATERIALS—  STRENG7^H  OF   THE   STRUCTURE.         135 

and  the  maximum  possible  stress  on  the  inner  ring  is 


•      (23) 
.      (24) 


and  the  ratio  of  inner  and  outer  radii  is 


Of  these  two  formulas,  the  first  gives  the  larger  and  conse- 
quently safer  results,  and,  in  the  absence  of  certain  knowledge 
of  the  distribution  of  pressure  within  the  walls  of  the  cylinder, 
is  perhaps  best. 

For  thick  spheres,  Lame's  formula  becomes 


2'f-A' 


<*» 


(27) 


Clark's  formula*  is  more  recent  than  the  preceding.  It  is 
assumed  that  the  expansion  of  concentric  rings  into  which  the 
cylinder  may  be  conceived  to  be  divided  is  inversely  as  their 
radii,  and  that  the  curve  of  stress  will  become  parabolic  if  so 
laid  down  that  the  radii  shall  be  taken  as  abscissas  and  the 
stresses  as  ordinates,  the  total  resistance  thus  varying  as  the 

*  Rules  and  Tables,  p.  687. 


136  THE   STEAM-BOILER. 

logarithm  of  the  ratio  of  the  radii.     Then  if  the  elastic  limit  be 
coincident  with  the  ultimate  strength,  and 

T  —  the  tenacity  of  the  metal, 

R  =  the  ratio,  external  diameter  divided  by  internal, 

p  =  the  bursting  pressure, 


(28) 


t 
R  —  eT  ...........     (29) 

In  other  cases,  instead  of  T  take  the  value  of  the  resistance 
at  the  elastic  limit,  and  base  the  calculation  of  proportions  upon 
the  elastic  limit  and  its  appropriate  factor  of  safety.  The  for- 
mulas as  given  are  considered  applicable  to  cast-iron. 

The  strength  of  thick  cast  cylinders  with  heads  cast  in  may, 
however,  sometimes  be  far  in  excess  even  of  the  calculated  re- 
sistance of  thin  cylinders.  The  formulas  for  thick  cylinders 
appear  to  be  in  error  on  the  safe  side  ;  and  very  greatly  so 
when,  as  is  usually  the  case,  the  cylinder  is  short,  and  strength- 
ened by  having  a  head  cast  in..  Such  cylinders  are  generally 
also  strengthened  by  very  heavy  flanges  at  the  open  end. 

The  Pressure  allowed  by  Law  or  by  government  regulations 
on  any  cylindrical  shell  is  found  by  the  following  rule  : 

"  Multiply  one  sixth  (-J-)  of  the  lowest  tensile  strength  found 
stamped  on  any  plate  in  the  cylindrical  shell  by  the  thickness  — 
expressed  in  inches  or  parts  of  an  inch  —  of  the  thinnest  plate 
in  the  same  cylindrical  shell,  and  divide  by  the  radius  or  half 
diameter  —  also  expressed  in  inches  —  and  the  sum  will  be  the 
pressure  allowable  per  square  inch  of  surface  for  single-riveting, 
to  which  add  20  per  centum  for  double-riveting." 

The  hydrostatic  pressure  applied  under  the  above  table  and 
rule  must  be  in  the  proportion  of  150  pounds  to  the  square 
inch  to  100  pounds  to  the  square  inch  of  the  working  pressure 
allowed. 

The  following  table  gives  the  pressures  thus  calculated  fpr 
single-riveted  boilers  of  various  sizes  : 


MATERIALS— STRENGTH   OF    THE   STRUCTURE.         137 


TABLE  OF  PRESSURES  ALLOWABLE  ON  BOILERS  MADE  SINCE  FEB- 
RUARY 28,   1872. 


45,000  TEN- 

50,000 TEN- 

55,000 TEN- 

6o,000 T  EN- 

65,000  TEN- 

70,000 TEN- 

SILE 

SILE 

SILE 

SI  LZ 

SILE 

SILE 

y 

jo 

STRENGTH. 

STRENGTH. 

STRENGTH. 

STRENGTH. 

STRENGTH. 

STRENGTH. 

'3 

CTl 

£ 

i  7,5oo 

4,8,333.3 

|,9,i66.6 

i,  10,000 

4,  10,833.3 

i,  11,666.6 

] 

"o 

i 

| 

3  -a 
8| 

i 

11 

si 

0*3 

8.1 

g 

go 
y  O 

jj 

c"3 

•£ 

. 

§| 

8 
1 

1 
_« 

1 

O  *O 

ii 

1 

ii 

3 

1/-3 

Q.T-I 

i 

i 

k'-S 

s 

£ 

^s 

£ 

r 

£ 

g* 

1 

p 

£ 

I* 

1 

8* 

-i875 

78.12 

93-74 

86.8 

104.  16 

95-48 

"4-57 

104.  16 

124.99 

ii2.84ii35.4 

121.52 

145.82 

.21 

87-5 

105. 

97.21 

116.65 

106.94 

128.3 

116.66 

139-99 

126.38  151.65 

136.11 

J63.33 

•23 

95-83 

114.99 

106.47 

127.76 

117.  12 

140.54 

127.77 

153-32 

138.41  166.05 

149.07 

178.88 

•25 

104.  16 

124.99 

ii5-74 

138.88 

127.31 

152.77 

138.88 

166.65 

150.46  180.55 

162.03 

193-43 

36 

.26 

108.33 

129.99 

120.37 

144.44 

132.4 

158.88 

144.44 

173.32 

156.48  187.77 

168.51 

2O2  .  2  I 

Inches. 

.29 

120.83 

!44-99 

i34-25 

161  .  ii 

147.68 

177.21 

161  .  ii 

193-33 

174.53  209.43 

187.90 

225.48 

-3125 

130.2 

156.24 

144.67 

173-6 

159.I4 

190.96 

173-6 

208.32 

188.07225.68 

202  5 

243.04 

•33 

137-5 

165- 

152-77 

183.3; 

168.05 

201.66 

183-33 

219.99 

198.61  238.35 

213.88 

256.65 

•35 

145-83 

174.99 

162.03 

194-43 

178.23 

213.87 

194.44 

233-32 

210.64,252.76 

226.84 

272.20 

•375 

156.2, 

187.5 

173.61 

208.33 

190.97 

229.  16 

208.33  249-99 

225  69 

271.82 

243-05 

291.66 

•1875 

74.01 

88.89 

82.23 

98.67 

90.46 

108.54 

98.68  118.41 

106.9 

128.28 

"5-13 

138.16 

.21 

82.89 

99.46 

92  i 

110.52 

101  .31 

121.57 

110.521132.62 

"9-73 

!43-67 

128^93 

I54-71 

•23 

90.78  108.03 

100.87 

121.04 

H0.96 

i33-!5 

121.  05(145.  2t 

131.-  13 

157-35 

141.22 

169.46 

•25 

98.68  118.41 

109  64 

131.56 

120.61 

144-73 

142.54 

171  .04 

153-5 

184.20 

38 
Inches. 

.26 
.29 

IO2  .  63 
114.47 

123.15 
I37-36 

114.03 
127.19 

136.83  125.43 
152.62  139.91 

136-84 
I52-63 

164.2 

183.15 

148.24 
165-35 

177  88 
198.42 

159-64 
178.06 

191  .56 
213.67 

•3125 

123.35    148.02 

164.46 

150.76 

180.91 

I64-47 

197.36 

178.17 

213-8 

191.88 

230.25 

•33 

130.26   156.31 

144-73 

173-67 

159.2 

191.04 

173-68 

208.41 

188.15 

225.78 

202  .  62 

243-14 

•35 

138.15 

165.78 

153-5 

184.21 

168.85 

202.62 

184.21 

221  .05 

199-56 

239-47 

214.91 

257-89 

•375 

I48. 

177.60 

l64  73 

197.67 

180.81 

217.09 

'97-36 

236.83 

213.81 

256-57 

230.26 

276.31 

•1875 

70-31 

84-37 

78.12 

93-74 

85.93 

103  .  i  i 

93-75 

II2.5 

101  .56 

121.87 

109-37 

131.24 

.21 

78.75 

94-50 

87.49 

104.98 

96.24 

115-48 

105. 

126. 

'13-74 

136.48 

122.49 

146.98 

•23 

86.25 

95-83 

114.99 

105.41 

126.49 

138. 

124.58  149.49 

160.99 

•25 

93-75 

112.5 

104.16 

124.99 

114.58 

137-49 

125- 

I50. 

135.41  162.49 

M5-83 

174-99 

40 

.26 

97-5 

117. 

108.33 

129.99 

119.  16 

142.99 

130. 

156. 

140.83  168.99 

151  .66 

181.99 

Inches. 

•29 

108.75 

130-5 

120.83 

144.99 

132.91 

159-49 

*4f-' 

174. 

157-08  188.49 

169.16 

202.99 

3"5 

117.18 

140.61 

130.2 

156.24 

143.22 

171.86 

156-25 

187.45 

169.27  203.12 

182.29 

218.74 

•33 

I23-75 

148.5 

137-49 

164.98 

151.24 

181.48 

165- 

I98. 

178.74  214.48 

192.49 

230  98 

•35 

131-25 

157-5 

145-83 

174.99 

160.41 

192.49 

210. 

189.58227.49 

204.  16 

244.99 

•375 

140.62 

168.74 

156.24 

187.48 

171.87 

206  .  24 

187-5 

225. 

2O3  .  I  2 

243-74 

218.74 

262.48 

•1875 

66.96 

80.35 

74.40 

89.28 

81.84 

98.20 

89.28 

107.13 

96.72 

116.06 

104.  16 

124.99 

.21 

75- 

90. 

83-32 

99-99 

91.66 

109.99 

IOO. 

1  2O. 

108.33,129.99 

116.66 

139-99 

•23 

.82.14 

98-56 

91.23 

109.51 

100.39 

120.46 

109.52 

131.42 

118.65:142.38 

127.77 

•25 

89.28 

107.13 

99-2 

119.04 

IO9  .  I  2 

130-94 

119.04 

142.84 

128.96    154-75 

138.88 

166.65 

42 

.26 

92.85 

111.42 

103.17 

123.8 

113-49 

136.18 

123.8 

148.56 

134.  12 

160.94 

144-44 

173-32 

Inches. 

.29 

103.57 

124.28 

115.07 

138.08 

126.57 

151-85 

138-09 

165.7 

149.6 

179-52 

i6i.n 

193-33 

•3125 

in  .6 

133-92 

124. 

148.8 

136.4 

16^.68 

148.741178.56 

161.2 

193-44 

173.61 

208  .  23 

•33 

117.85 

141.42 

130.94 

157.12 

114.04 

172.84 

157.14188.56 

170.23  204.27 

183-33 

219.99 

•35 

125 

150. 

138.88 

166.65 

152.77 

183-32 

166.66  199.99 

i8o.55'2i6.66 

194.44 

233.32 

•375 

133-92 

160.7 

148.8 

178-56 

163.68 

196.40 

I78-57 

214.28 

193-45232.14 

208.33 

249  99 

•1875 

63.92 

76.7 

71  .01 

85.22 

78.12 

93-74 

85.22 

IO2  .  26 

92.32  110.78 

99.42 

"9-3 

.2T 

71-59 

85-9 

79-54 

95-44 

87.49 

104.98 

95.451114.54 

103.4    124.08 

in  .36 

133-63 

•23 

78.4 

94.08 

87.12 

104-54 

95.83 

114.99 

104.54  125.44 

113-25 

'35-9 

121.96 

146.35 

•25 

85.22 

102.26 

94.69 

113.62 

104.  16 

124.99 

113.63  136.35 

123.1 

147.72 

132.56 

159-07 

44 

.26 

88.63  106.35 

98.48 

118.17 

108.33 

129.99 

118.18141.81 

128.02 

153-62 

137-87 

165.44 

Inches. 

.29 

98.86  118.63  109.84 

131.80 

120.83 

144-99 

131.81  158.17 

142-79 

I7I-33 

I53-78 

184-53 

•3*25 

106.53 

127.83  118.36 

142.03 

130.2 

156.24 

142.04  170.44 

153.88 

184.65 

165.71 

198-85 

•33 

112.5 

135- 

124.99 

149.98 

137-49 

164,98 

150.     Ii8o. 

162.49 

194.98 

174.99 

209.98 

•35 
•375 

119.31 
127.81 

143.17  132.57 
153.37  142.04 

159.08 
170.44 

145-83  '74  99 
156.24  187.48 

159.09  190.9 
170.45^04.54 

8$ 

206.8 
221.58 

185.6    222.72 
198.861238.63 

138 


THE   STEAM-BOILER. 


TABLE  OF  PRESSURES  ALLOWABLE  ON  BOILERS   MADE   SINCE  FEB- 
RUARY 28,   1872.— Continued. 


45,000  TEN- 

50,000 TEN- 

55,000 TEN- 

60,000 TEN- 

65,000 TEN- 

70,000 TEN- 

SILE 

SILE 

SILE 

SILE 

SILE 

SILE 

tj 

8 

STRENGTH. 

STRENGTH. 

STRENGTH. 

STRENGTH. 

STRENGTH. 

STRENGTH. 

1 

rt 

K 

4,  7,5oo 

4,8,333-3 

i  9.166.6 

g,     10,000 

i  10,833.3 

&,  11,666.6 

0 

"o 

gc 

SG  c 

c"rt 
<U  G 

Si 

11 

sl 

§ 

1 

i 

tj  O 

i 

o 

=5 

u  .- 

£ 

y-B 

i 

m 

"- 

| 

o  o 

e 

.3 

1 

i 

o.| 

I 

0? 

1 

| 

S| 

8 

8| 

1 

a| 

Q 

H 

OH 

o 

£ 

8' 

£ 

O 

OH 

8rt 

£ 

8* 

£ 

8 

•  1875 

61.14 

73-36 

67-93 

81.51 

74.72 

89.66 

81.51 

97.81 

88.31 

105.97 

95-i 

114.12 

.21 

68.47 

82.16 

76.08 

91.29 

83-69 

100.42 

91.3 

109.56 

98.91 

118.69 

106.52 

127.82 

•23 

75- 

90. 

83.33  ioo. 

91.66 

109.99 

IOO. 

120. 

108.33 

129.99 

116.66 

x39-99 

•25 

81.51 

97.81 

90.57,108.68 

99-63 

"9-55 

108.69 

130.42 

"7-75 

141-3 

126.8 

152.16 

46 

.26 

81.78 

101.73 

94.2   113.04 

103  .  62 

I24-34 

"3-44 

I35  -64 

122.46 

140-93 

131.88 

158-25. 

Inches 

.29 

94-56 

IJ3-47 

105.07  126. 

"5-57 

138.68 

126.09  151.3 

136-59 

163.92 

147.1 

176.52 

•3I25 

101.9 

122.28 

113.21  135.86 

124.54 

149.44 

135.86  163  03 

147.19 

176.62 

158.51 

190.21 

•33 

107.6 

129.  12 

119.56  143.47 

131.52 

157.82 

143  97 

172.16 

155-43 

186.51 

167-39 

200.86 

•35 

"4-13 

136.95 

126.8    152.16 

139-49 

167.38 

152.17 

182.6 

164.85 

197.82 

I77-53 

213.03 

•375 

122.28 

I46-73 

135.86  163.03  149.45 

179-34 

163.04 

I95-64 

176.62 

211.94 

190.21 

228.25 

•1875 

58.59 

70.30 

65.1 

78.12 

71.61 

85-93 

78.12 

93-74 

84.63 

101.55 

~9^i3 

iog-35 

.21 

65.62 

78.74 

72.91 

87-49 

80.2 

96.24 

87.49 

104.98 

94-79 

"3-74 

102.08 

122.49 

•23 

71.87 

86.24 

79.85  95.82 

87.84 

105.4 

95.83  114.99 

103.81 

I24-57 

in.  8 

133.16 

•25 

78.12 

93-74 

86.8    104  16 

95-48 

"4-57 

104.16  124.99 

112.84 

135-4 

121.52 

145-82 

48 

.26 

81.25 

97-50 

90.271108.32 

99-3 

119.  16 

108  .  33  129.99 

117.36 

140.83 

126.38 

15I-65 

Inches. 

.29 

90.62 

108.74 

100.69 

120.82 

110.76 

132.91 

120.83  144.99 

130.9 

157-08 

140.97 

169.16 

•3I25 

97-65 

117.18 

108.5 

130.2 

II9-35 

143.22 

130.21  i  156.25 

141.05 

169.26 

182.28 

•33 

103.12 

123.74 

114-58 

137-49 

126.04 

151.24 

137-5    165- 

148.95 

178.74 

160.41 

192.49 

•35 

I09-37 

131.24 

121.52 

145-82 

133-67 

160.4 

145.83  174.99 

I57-98 

189.57 

170.13 

204.15 

•375 

117.18 

140.61 

130.2 

156-24 

143.22 

171.86 

156.25^187.50 

169.27 

203.12 

182.29 

218.74 

•1875 

52.08 

62.49 

57-87 

69-44 

63-65 

76.38 

69.44 

82.44 

75-23 

90.27 

81.01 

97.21 

.21 

58.33 

69.99 

64.81 

77-77 

71.29 

85-54 

77-77 

93-32 

84-25 

IOI.  I 

90.74 

108.88. 

•23 

63.88 

76-65 

70.98 

85-17 

78.08 

93-69 

85.18  102.21 

92.28 

110.73 

99-38 

119.25 

•25 

69.44 

83-32 

77.16 

92.59 

84.87 

01.84 

92.59  in.  10 

100.3 

120.36 

108.02 

129.62 

54 

.26 

72.22 

86.66 

80.24    96-28 

88.27 

05.92 

96.29  115.54 

104.31 

125.17 

112.44 

134.8 

Inches. 

.20 

80.55 

96.66 

89.5  (107.40 

98.45 

18.14 

107.41:128.88 

116.35 

139.62 

125.3 

150.36 

•3125 

86  8 

104.  16 

96.44  115.72 

106.09 

27.30 

II5-55ll38.66 

125.38 

150.45 

135-03 

162.03 

•33 

91.66 

109  99 

IOI  .84   122.22 

112.03 

34-43 

122.22   146.66 

132-4 

158.88 

142.59 

171.10 

•35 

97.22 

116.66 

:o8.o2  129.62 

118.82 

42-58 

129.62  155.54 

140.43 

168.51 

151.23 

181.47 

•375 

104.  16 

124.99 

115.74  138.88 

127.31 

152.77 

138.88  166.65 

150.46 

180.55 

162.03 

194-43 

•1875 

46.87 

56.24 

52.08   62.49 

57-29 

68.74 

62.5 

75- 

67.7 

81.24 

72.91 

87.49 

.21 

52-5 

63- 

58.33  69.99 

64.16 

76.99 

69.99  84: 

75-83 

90-99 

81.66 

97-99- 

•23 

57-5 

69. 

63.88;  76.65 

70.27 

84.32 

76.66    91.99 

83.05 

99-66 

89.44 

107.32 

.25 

62.5 

75- 

69.44  83.32 

76.38 

91.65 

83-331  99-99 

90.27 

108.32 

97.22 

116.66 

60 

.26 

65- 

78. 

72.22    86.66 

79-44 

95-32 

86.66!io3.gg 

93-88 

112.65 

IOI.  1  1 

121.33 

Inches. 

.29 

72-5 

87. 

80.55    96.66 

88.  61 

106.33 

96.66 

"5-99 

104.72 

125.66 

112.77 

•3125 

78.12 

93-74 

86.8    104.16 

95.48 

"4-57 

104.18 

124.99 

112  .95 

135-54 

121  .52 

145-82 

•33 

82.5 

99- 

91.66  109.99 

100.83 

120.99 

109.99 

132. 

119.  1  6 

142.99 

128.33 

*53-99 

87.5 

105. 

97.22  116.66 

106.94 

128.32 

116.66 

139-99 

126.38 

136.11,163.33 

•375 

93-75 

112.5 

104.16  124.99 

114.58 

*37-49 

125. 

150. 

I35-4I 

162.49 

145-83 

175-99 

.1875 

42.61 

5I-I3 

47-34    56.8 

52.07 

62.49 

56.81 

68.17 

6i-55 

73-86 

66.28 

79  -5S 

.21 

47.72 

57.26 

53-        63.63 

58  33 

69.99 

63-63 

76.35    68.93 

82.71 

74-24 

89  .  08 

•23 

52.27 

62.72 

58. 

69.69 

63.88 

76.65 

69.69 

83-62!    75-5 

90.6 

81.31'  97-57 

•25 

56.81 

68.17 

63-J3 

75-75 

69.44 

83.32 

75-75 

90.90    82.07 

98.48 

88.37  106.04 

66 
Inches. 

.26 
•29 

59-09 
65.90 

70.9 
79.08 

65.65 
73-23 

78.78 
87.87 

72.22 
80.55 

86  66 
96.66 

78.78 
87-87 

94-53 
105.44 

85-35 
95-z 

IO2  .  42 
114.24 

91.91  110.29 
102.52  123.02 

•3125 

71- 

85.2 

78.91 

94-69 

86.89 

104.  16 

94  69 

113.62 

102.58  123.09 

110.47  !32-56 

•33 

75- 

90. 

83-33 

99-99 

91.66 

109.99 

99-99 

120. 

108.33  129.90 

116.66  139.99 

•35 

79-56 

95-47 

88.38 

106.05 

97.22 

116.66 

106. 

127.27 

114.89 

137.86 

123.73  148.47 

•375 

85.22 

102.26 

94-69 

113.62 

104.16 

124.99 

113.62 

136.34 

123.1 

I47.72 

132-57 

159-08 

MATERIALS— STRENGTH  OF   THE    STRUCTURE.         139 


TABLE  OF  PRESSURES  ALLOWABLE  ON   BOILERS   MADE   SINCE  FEB- 
RUARY  28,  1872.— Continued. 


45,000  TEN- 

50,000 TEN- 

55,000 TEN- 

60,000 TEN- 

65,000 TEN- 

70,000 TEN- 

SILE 

SILE 

SILE 

SILE 

SILE 

SILE 

LJ 

1 

STRENGTH. 

STRENGTH. 

STRENGTH. 

STRENGTH. 

STRENGTH. 

STRENGTH. 

a 

3 

B,    7,500 

4,  8,333-3 

|,  9.166.6 

B,     10,000 

4,  10,833.3 

4,  11,666.6 

« 

£ 

CQ 
*O 

"o 

o"3 

~3 

C  "c4 

«_• 

c  'x 

c*rt 

1 

<U 

'* 

i 

§  c 

d 

S§ 

i 

§  a 
u.2 

oJ 

c 

w  c 

if! 

5  c 

5 

H 

*1 

? 

i 

i 

8* 

I 

E 

PL,  ' 

3 

<u 

8rt 

£ 

8* 

I 

i 

8* 

.1875 

39.06 

46.87 

43-4 

52.08 

47-74 

57.28 

52.08 

62.49 

56.42 

67.70 

60.76 

72.91 

.21 

43-75 

52.5 

48.6 

58-331   53-47 

64.16 

58.33 

69-99 

63.19 

75-82 

68  05 

81.66 

•23 

47.91 

57-49 

53-24 

63.88 

58-56 

70.27 

63.88 

76.65 

62.21 

83-05 

74-53 

89.43 

•25 

52.08 

62.49 

57-87 

69.44 

63.65 

76.38 

69.44 

83-32 

75-22 

90.26 

81.01 

97-21 

72 

.26 

54.16 

64.99 

60.  18 

72.21 

66.2 

79-44 

72.22 

86.66 

76.94 

93-88 

84-25 

105.10 

Inches. 

•29 

60.41 

72.49 

67.  12 

80.54 

73-84 

88.60 

80.55 

96.66 

87.26 

104.71 

93-98 

112.77 

.3125 

65.10 

78.12 

72-33 

86.8 

79-57 

95.48 

86.8 

104.  16 

94.03 

112    83 

101  .27 

121.52 

•33 

68  75 

82.5 

76.38 

91.65 

84.02 

100.82 

91.66 

109.99 

99  3 

119.16 

106.94 

128.32 

•35 

72.91 

87.49 

Sl.OI 

97.21 

89.11 

106.93 

97.22 

116.66 

105.32 

126.38 

113.42 

136.  i 

•375 

78.12 

93-74 

86.8 

104.  i  6 

95.48 

i'4-57 

104.  16 

124.99 

112.84 

135-43 

121    52 

145.82 

•i875 

36.05 

43-21 

40.06 

48.07 

44.07 

52.87 

48.07 

57.68 

52.08 

62.49 

56.08 

67.29- 

.21 

40.38 

48.45 

44.87 

53-84!   49-35 

59-22 

51-84 

64.60 

58.33 

69.99 

62.82 

75-38 

•23 
.25 

44-23 
48.07 

53-07 
57-68 

53  41 

58.96    54-05 
64-09    58-76 

64.86 
70.5 

58-95 
64.4 

70.76 
76.92 

63.88 
69.44 

76.65 
83.32 

68.80 
74.78 

82.56 
89  73 

78 

.26 

50. 

60. 

55-55 

66.66    66.11 

73-33 

66.66 

79-99 

72.22 

86.66 

77-77 

93  32 

Inches. 

•29 

55  76 
60.09 

66.91 
72.1 

66.77 

74.35!  68.16 
80.12    73.45 

81.79 
88.14 

74-35 
80.12 

89.22 
96.14 

80.55 
86.8 

96.66 
104.  16 

86.75 
93-48 

104.1 
112.17 

•33 

63.46 

76.15 

70.51 

84.61    77.56 

93-07 

84.61 

101.  S3 

91.66 

109.99 

98.71 

118.45 

•35 

67-3 

80.76 

74-78 

89.73    82.26 

98.71 

89  74 

107.68 

97.22 

116.66 

104.70 

125.64 

•375 

72.11 

86.53 

80.12 

96.14    88.14 

105.76 

96.15 

115-38 

104.  16 

124.99 

112.17 

134  6 

•1875 

33-48 

40.17 

37.2 

44.68)  40.92 

49  i 

44.64 

53-56 

48-36 

58.03 

52.08 

62.49 

.21 

37-5 

45- 

41.66 

49  99!   45.83 

54-95 

50- 

60. 

54.16 

64  99 

58.33 

69.99 

•23 

41.02 

49.22 

45-63 

54.75!   50.19 

60.22 

54-75 

65  71 

59-32 

71.18 

63-65 

76.38 

•25 

44.64 

53-56 

49-6 

59.52     54.56 

65-47 

59-52 

71.42 

64.48 

77-37 

69.44 

83-32 

84 

.26 

46.42 

55-7 

5I-58 

61.89    56.74 

68.08 

61  .9 

74.28 

67.05 

80.46 

72.22 

86.66 

Inches. 

.29 

51-78 

62.13 

57-53 

69.03    63.29 

75  94 

69.04 

82.84 

74-8 

89.76 

80.55 

96.66 

•3125 

55-8 

66.96 

62. 

74-4      68.2 

81.84 

74-4 

89.28 

80.6 

96.72 

86.8 

104.16 

•33 

58.92 

70.7 

65-47 

78.56:   72.02 

86.42 

78.57 

94.28 

85.11 

IO2.  13 

91.66 

109.99 

•35 

62.5 

75- 

69.44 

83.32!   76.38 

9i  65 

83-33 

99-99 

90.27 

108  .  32 

97.22 

116.66 

•375 

66.96 

80.35 

74  4 

89.28 

81.84 

98.2 

89.28 

107.13 

96.72 

116.06 

104  16 

124.99 

•1875 

31-25 

37-5 

34-72 

41.66 

38.19 

45-82 

41.66 

49-99 

45-13 

54-15 

48.68 

58.33 

.21 

35- 

42. 

38.88 

46-65 

42.77 

51-32 

46.66 

55-99 

50.55 

60.66 

54-44 

65-32 

•23 

38.33 

45-99 

42-59 

51  .  10 

46-85 

56.22 

Si-" 

6i-33 

55-37 

66.44 

59.62 

71.54 

90 

:S 

41.66 
43-33 

49-99 
51-99 

46.29 
48.14 

55-54 
57-76 

50.92 
52.96 

61.1 
63  55 

55-55 
57-77 

66.66 
69.32 

60.  18 
62.59 

72.21 
75-i 

64.81 
67.4 

77-77 
80.88 

Inches. 

.29 

48.33 

57-99 

53-7 

64.44 

59-07 

70.8 

64.44 

77-32 

69.81 

83-77 

75-i8 

90.21 

•3125 

52.08 

62.49 

57.86 

69-43 

63.65 

76.38 

69.44 

83-32 

75-23 

90.27 

81.01 

97-21 

•33 

55- 

66. 

6i.ii 

73-33 

67.22 

80.66 

73-33 

87-99 

79-44 

95-32 

85-55 

102.66 

•35 

58.33 

69  99 

64.81 

77-77 

71.29 

85-54 

77-77 

93-32 

84-25 

IOI.I 

go.  72 

108.88 

•375 

62.5 

75- 

69.44 

83-32 

76.38 

91.65 

83-33 

99-99 

90.27 

108.32 

97.22 

116.66 

•1875 

29.29 

35-14 

32-55 

39.06 

35  8 

42.96 

39-06 

46.87 

42-31 

50.77 

45-57 

54-68 

.31 

32.81 

39-37 

36-45 

43-74 

40.1 

48.12 

43-75 

52.5 

47-39 

^6.86 

51-04 

61.  24 

•23 

35-93 

43.11 

39-93 

47-91 

43-92 

52.7 

47-91 

57-49 

51-9 

62.28 

55-9 

67  08 

•25 

39.06 

46.87 

43-4 

52.08 

47-74 

57-28 

52.08 

62.49 

56-42 

67.67 

60.76 

72.91 

96 

.26 

40.62 

48.74 

54  16 

49-65 

59-68 

54.16 

64.99 

58-78 

70-53 

63.19 

75-82 

Inches. 

•29 

45-31 

54  37 

50-34 

60.4 

55.38 

66.45 

60.41 

72.49 

65-45 

78.54 

70.48 

84-57 

•3125 

48  82 

58-58 

54-25 

65-1 

59.67 

71.6 

65.1 

78.12 

70.52 

84.62 

75-95 

91.14 

•33 
•35 

51-56 
54-68 

61.87 
65-61 

57-29 
60.76 

68.74 
72-91 

63.02 
66.83 

75.62 
80.19 

68.75 
72.91 

82.5 

87.49 

74-47 
78.99 

89-36 
94-78 

80.2 
85.06 

96.24 
102.07 

•375 

58-58 

70.29 

65.1 

78.12 

71  .61 

85-93 

78.12 

93  74 

84.63 

101-55 

91.14 

109.6 

140  THE   STEAM-BOILER. 

Externally-fired  boilers  are  not  permitted  by  United  States 
regulations  to  be  made  thicker  than  0.51  inch  (1.2  cm.).  The 
20  per  cent  higher  pressure  of  the  table  is  allowed  on  steam- 
vessels  which  carry  no  passengers.  It  will  be  observed  that 
the  rule  above  given  allows  an  apparent  "  factor  of  safety"  of 
six;  while  the  loss  of  strength  at  a  single-riveted  seam  reduces 
it  to  the  actual  value  of  four,  nearly.  It  would  probably  be  on 
the  whole  wiser  to  use  as  the  actual  value  the  higher  figure, 
and  thus  to  reduce  the  pressures  carried  to  one  third  below 
those  now  permitted,  except  where  inspection  and  test  during 
construction,  and  constant  supervision  with  frequent  inspection 
during  the  life  of  the  boiler,  may  give  a  safe  margin  with  the 
lower  figure.  The  operation  of  the  law  \vhich  allows  old  boilers 
to  carry  two  thirds  the  test  pressure  is  to  reduce  the  real  factor 
often  to  less  than  one  and  a  half  ;  for  it  is  well  known  that 
iron  will  not  carry  permanently  a  load  which  it  will  sustain  for 
a  short  time  without  observable  yielding. 

French  regulations  make  the  thickness  of  wrought-iron 
cylindrical  shells  of  boilers  not  less  than 


t  — 


in  millimetres,  when  the  pressure,  /,  is  in  atmospheres  and  the 
diameter,  d,  is  in  metres.     In  no  case,  however,  is  a  greater 
thickness  allowed  than  15  mm.  (0.6  in.). 
German  regulations  give 

t  =  o.ooi^       o.i  inches. 


Flues  and  Cylinders  subjected  to  external  pressure  resist 
that  pressure  in  proportion  to  their  stiffness  and  their  com- 
pressive  strength  if  thin,  and  if  thick  sustain  a  pressure  pro- 
portional to  their  thickness  and  maximum  resistance  to  crush- 
ing. 

Fairbairn,*  experimenting  on  flues  of  thin  iron,  0.04  inch 

*  Useful  Information.     Second  Series. 


MATERIALS— STRENGTH   OF    THE    STRUCTURE.         14  I 

(0.102  centimetre),  of  small  diameter,  4  inches  (10.2  centi- 
metres) to  12  (31  centimetres),  and  from  20  inches  (50.8  centi- 
metres) to  5  feet  (1.52  metres)  long,  found  that  their  resistance 
to  collapse  varied  inversely  as  the  product  of  their  lengths  and 
their  diameters,  and  directly  as  the  2.19  power  of  their  thick- 
ness. 

The  following  equation  fairly  expressed  his  results  when/ 
is  the  external  pressure  in  pounds  per  square  inch,  /  their  thick- 
ness in  inches,  d  their  diameter,  and  L  the  length  in  feet : 


or,  for  the  length  in  inches, 

P  =  9>672,ooo-9 (2) 


In  metric  measures,  kilogrammes  and  centimetres  diameter, 
and  metres  of  length, 

/  =  68,000—,  nearly (3) 

rT~ 

68,000 k) 


2. 
t    = 


For  elliptical  flues  take  d  =  ~- ;  where  a  is  the  greater  and 

b  the  lesser  semi-axis. 

These  equations  probably  give  too  small   values   of  t  for 
heavy  flues  under  high  pressure. 

Belpaire's  rule,  deduced  from  Fairbairn's  experiments,  is 


^2.081 
p=  i(o57,i80— ~ (5) 


142  THE   STEAM-BOILER. 

Lloyd's  rule  for  flues  is 


in  which  a  is  made  89,600  pounds  per  square  inch. 

The  British  Board  of  Trade  Rule  is,  for  cylindrical  furnaces 
with  butted  joints, 


in  which  a  is  90,000,  provided,  always, 


<  8,000^; 


and  *for  large  joints  a  —  70,000,  unless  bevelled  to  a  true  circle, 
when  a  =  80,000.  If  the  work  is  not  of  the  best  quality,  these 
values  of  a  are  reduced  to  80,000,  60,000,  and  70,000. 

Flanged  and  Corrugated  Flues  are  much  stronger  than  plain, 
lapped,  or  butt-jointed  flues.  Experiment  indicates  that  it  is 
allowable  to  consider  the  length  L  in  the  formulae  for  strength 
of  f]ues  as  the,  distance  from  flange  to  flange,  and  to  assume 
that  the  flanges  support  the  flue  as  effectively  as  the  flue 
sheets.  Where  the  several  courses  of  a  flue  are  flanged  to- 
gether instead  of  being  connected  by  the  usual  lap-jointed 
girth-seams,  the  strength  of  the  flue  is  thus  enormously  in- 
creased. Another  method  of  strengthening  the  flue  is  by  sur- 
rounding it,  at  intervals,  with  a  strongly  made  ring  of  angle  or 
T-iron,  which  answers  the  purpose  of  a  flange,  while  being  less 
costly  in  construction.  To  prevent  injury  by  overheating  at 
those  parts  where  the  total  thickness  of  metal  traversed  by  the 
heat  from  the  furnace-gases  would  be  objectionably  great,  the 
ring  is  often  supported  clear  of  the  flue  by  a  set  of  thimbles 
through  which  the  rivets  holding  it  in  place  are  driven. 

The  corrugated  flue  is  now  very  extensively  used,  the  cor- 
rugations^ extending  around  the  flue  and  having  a  pitch  of  ten 


MATERIALS-^-STRENGTH  OF    THE   STRUCTURE.         143 

or  twelve  times  the  thickness  of  the  sheet.  These  flues  pos- 
sess the  double  advantage  of  having  more  than  twice  the 
strength  of  equally  heavy  plain  flues,  and  of  being  so  much 
thinner  for  a  given  strength  as  to  be  vastly  safer  against  over- 
heating and  burning.  These  flues  are  less  liable  to  distortion 
in  the  processes  of  working  than  are  plain  flues. 

By  the  United  States  regulations,  lap-welded  flues  less  than 
1  8  feet  long  and  7  inches  or  more  in  diameter  are  allowed  to 
carry  pressures  determined  by  the  formula 

ct  pr 

P  =  -;    *==--; 
r  c 

in  which  the  pressure,  p,  is  in  pounds  per  square  inch  ;  the 
thickness,  /,  and  the  radius,  r,  of  the  flue  in  inches.  The  value 
of  the  constant  c  is  44.  This  gives,  for  example,  an  allowable 
pressure  of  200  pounds  per  square  inch  on  a  flue  14  inches  in 
diameter,  less  than  18  feet  long  and  0.32  thick.  A  minimum 
thickness  is  set  at 


For  lap-welded  flues  exceeding  18  feet  in  length,  3  pounds  is 
deducted  from  the  pressure  calculated  as  above,  for  each  added 
foot,  or  o.oi  inch  is  added  to  its  thickness.  When  between  7 
and  1  6  inches  diameter  and  5  to  10  feet  long,  one  strengthen- 
ing ring  is  required  ;  and  where  10  to  15  feet  long,  two  such 
rings,  each  of  a  thickness  of  metal  at  least  equal  to  that  of  the 
flue,  and  2^  inches  or  more  in  width. 

Flues  16  to  40  inches  diameter  are  allowed  by  the  United 
States  regulations  a  pressure 

>=<?. 

1760 
in  which/  =  --T—  ,  c  —  0.31,  or 


144  THE    STEAM-BOILER. 

which  allows  100  pounds  per  square  inch  on  a  ^ue  20  inches  in 
diameter  and  0.37  inch  thick. 

Corrugated  furnace-flues  are  allowed  to  "  carry"  a  pressure, 


P  =  I2'5oo~; 


equivalent  to  150  pounds  on  a  flue  40  inches  in  diameter  and 
0.5  inch  thick.  Other  flues  are  allowed  pressures  determined 
by  Fairbairn's  formula, 

, 

in  which,  however,  L  is  in  feet.  Rings  are  fitted  in  such  man- 
ner as  to  reduce  the  maximum  tension  on  the  rivets  to  6000 
pounds  per  square  inch  of  section. 

57.  Stayed  Surfaces  and  Stays  and  Braces  are  parts  and 
members  which,  in  steam-boiler  design  and  construction,  should 
be  studied  with  special  care.  Where  it  is  possible  to  make  the 
strength  of  the  structure  ample  by  correctly  forming  parts  ex- 
posed to  stress,  as  by  making  them  cylindrical,  it  is  usually  con- 
sidered best  to  do  so ;  but  in  many  types  of  boiler  this  is  im- 
practicable, and  staying  must  be  resorted  to.  Properly  designed 
stayed  surfaces  should  be  made  the  strongest  parts  of  the  boiler. 
The  fireboxes  of  locomotives  and  of  other  firebox  boilers,  in 
which  stay-bolts  are  well  distributed,  the  water-legs  of  many 
marine  boilers,  and  other  parts  composed  of  flat  surfaces  sus- 
tained by  stays  and  braces,  are  common  illustrations  of  the 
method  of  resisting  pressure. 

Where  flat  surfaces  are  secured  against  lateral  pressure  by 
stay-bolts,  as  is  done  in  steam-boilers,  these  bolts  may  yield 
either  by  breaking  across,  or  by  shearing  the  threads  of  the 
screw  in  the  bolt  or  in  the  sheet.  Such  bolts  should  not  be  so 
proportioned  that  they  are  equally  liable  to  break  by  either 
method,  but  should  be  given  a  large  factor  of  safety  (15  to  20) 
to  allow  for  reduction  of  size  by  corrosion,  from  which  kind  of 
deterioration  they  are  liable  to  suffer  seriously.  Wrought-iron 


MATERIALS—  STRENGTH   OF    THE    STRUCTURE.         145 

and  soft  steels  are  used  for  these  bolts.  They  are  screwed 
through  the  plate,  and  the  projecting  ends  are  usually  headed 
like  rivets.  Nuts  are  sometimes  screwed  on  them  instead  of 
riveting  them  when  they  are  not  liable  to  injury  by  flame. 

"  Button-set"  heads  are  from  25  to  35  stronger  than  the 
conical  hammered  head,  and  nuts  give  still  greater  strength. 

Experiments  made  by  Chief  Engineers  Sprague  and  Tower, 
for  the  U.  S.  Navy  Department,  lead  to  the  following  formula* 
and  values  of  the  coefficient  a,  p  being  the  safe  working  pres- 
sure, t  the  thickness  of  plate,  and  d  the  distance  from  bolt  to 
bolt: 


(0 


VALUES  OF  a  IN  BRITISH  AND  METRIC  MEASURES. 

A.  .         Am. 

For  iron  plates  and  bolts  .....................   24.000  1,693 

For  steel  plates  and  iron  bolts  ................   25,000  1,758 

For  steel  plates  and  steel  bolts  ...............   28,000  1,968 

For  iron  plates  and  iron  bolts  with  nuts  .......   40,000  2,812 

For  copper  plates  and  iron  bolts  ..............    14,500  1,020 

The  working  load  is  given  in  pounds  on  the  square  inch  and 
kilogrammes  per  square  centimetre,  the  measurements  being 
taken  in  inches  and  centimetres.  The  heads,  where  riveted, 
are  assumed  to  be  made  of  the  button  shape. 

The  diameter  of  stay  is  made  about  2  Vt,  the  number  of 
threads  per  inch  12,  or  14  (5  or  6  per  centimetre).  A  very  high 
factor  of  safety,  as  above,  is  recommended  for  stays,  to  afford 
ample  margin  for  loss  by  corrosion. 

Lloyd's  Rule  for  stayed  plates  is 


in  which  p  is  the  working  pressure  in  pounds  on  the  square 
inch,  /j  the  thickness  of  plate  in  sixteenths  of  an  inch,  and/,  is 
the  distance  apart  of  the  stays  in  inches. 


*  Report  on  Boiler  Bracing.     Washington,  1879. 


146  THE   STEAM-BOILER. 

The  coefficient  a  has  the  following  value : 

a  -^  90  for  plate  T7¥  inch  thick  or  less  ;  with  screw  stays 

and  riveted  heads  ; 
a  =  100  for   plate  T7F  inch  thick  or  more;  screw  stays 

and  riveted  heads  ; 
a  =  1 10  for  plate  T7-g-  inch  thick  or  less  ;  screw  stays  and 

nuts ; 
a  —  1 20  for  plate  ^  inch  thick  or  more  ;  screw  stays  and 

nuts  ; 
a  =  140  for  plate  T7-g-  inch  thick  or  more  ;  screw  stays 

with  double  nuts ; 
a  =  1 60  for  plate  T7T  inch  thick  ;  with  screw  stays  double 

nuts  and  washers. 

The  Board  of  Trade  of  Great  Britain  prescribes 


in  which  tl  is  the  thickness  of  plate  as  above,  and  s  is  the  area 
of  surface  supported,  in  square  inches. 

a  =  100  for  plates  not  exposed  to  heat,  and  fitted  with 
nuts  and  washers  of  3"  diameter  and  of  -f  the 
thickness  of  the  plates ; 

a  =  90  for  same  case,  but  with  nuts  only ; 

a  =  60  in  steam  and  having  nuts  and  washers ; 

a  —  54  if  with  nuts  only ; 

a  —  80  in  water  spaces,  with  screw  stays  and  nuts; 

a  —  60  if  with  screw  stays  riveted  ; 

a  =  36  in  steam,  screw  stays,  riveted. 

For  girder  stays, 


where  the  symbols  are  defined  as  on   page   148.     When  one. 


MATERIALS— STRENGTH   OF    THE    STRUCTURE.         147 

two  or  three,  or  four  bolts  carry  the  girder,  a  =  500,  750,  and 
800,  respectively. 

Stay-bolts  should  have  diameters  considerably  exceeding 
double  the  thickness  of  the  plate. 

D.  K.  Clark  allows,  as  a  maximum,  the  pressure 

tT 
P  =  4°7-> •    •    (5) 


where  t,  T,  and  d  are  the  thickness  of  sheet  and  its  tenacity, 
and  the  "  pitch  "  of  the  stays  in  inches. 

In  computing  the  strength  of  stayed  surfaces,  it  is  to  be  un- 
derstood that  each  stay  sustains  the  pressure  on  an  area  bounded 
by  lines  drawn  midway  between  it  and  its  neighbors,  and  mea- 
sured by  the  product  of  the  distances  between  stays  in  the  two 
directions  of  the  lines  of  their  attachments  to  the  sheet.  Thus 
marine  boiler  stays  spaced  8  inches  apart  sustain  the  pressure 
on  64  square  inches  ;  while  locomotive  firebox  stay-bolts  spaced 
4^  inches  each  way  carry  the  pressure  on  2oJ  square  inches. 

A  common  minimum  factor  of  safety  for  stays,  stay-bolts, 
and  braces  is  8,  and  when  liable  to  serious  corrosion  the  load 
applied  is  often  reduced  to  3000  or  4000  pounds  per  square 
inch  of  section  of  stay  or  brace,  thus  giving  a  factor  of  ten  or 
more.  The  actual  rupture  of  stay-bolted  surfaces  was  found  by 
the  Author,  by  the  study  of  the  results  of  experimental  steam- 
boiler  explosions  in  1871,*  to  be  about  the  pressure 


f----\^dl'   •  • (6) 

in  which  /  is  the  thickness  of  plate,  and  d  the  pitch  of  the  stay- 
bolts.     In  design,  we  would  make 


(7) 


*  Journal  Franklin  Institute,  1872. 


143  THE   STEAM-BOILER. 

a  being  the  factor  of  safety,  which,  as  has  been  seen,  should  al- 
ways be  large,  and  /'  the  working  pressure. 

Fairbairn  showed  that  the  diameter  of  a  stay-bolt  should 
exceed  double  the  thickness  of  the  sheet  by  the  amount  to  be 
allowed  for  corrosion.  He  found  that  riveting  over  the  ends 
of  screwed  stays  increased  the  strength  of  the  construction  14 
per  cent. 

Where  the  crown-sheet  of  the  furnace  of  a  boiler  is  supported 
by  girders,  the  load  to  be  permitted  may  be  adjusted  by  the 
formula,  already  given, 

cd?t 


in  which 

w  =  width  of  the  fire-box  ; 
p'  —  the  pitch  of  the  supporting  bolts  ; 
d'  =  the  distance  from  centre  to  centre  of  girders  ; 
/  =  their  length  ; 
d  =  their  depth  ; 
t  =•  their  thickness  ; 

all  dimensions  in  inches  except  /,  which  is  taken  in  feet.  This 
is  the  formula  approved  by  the  British  Board  of  Trade.  The 
value  of  the  coefficient  c  is  from  500,  when  but  one  supporting 
bolt  is  used,  to  750  and  800  when  two  or  three  and  when  four 
bolts  are  employed. 

The  accompanying  figure  exhibits  a  common  form  of  stay 
for  water-legs  and  other  narrow  water  spaces. 
The  stay  is  cut  from  a  long  screwed  rod,  and 
is  frequently  fitted  with  a  nut  and  washer  at 
each  end.  They  are  sometimes  drilled  longi- 
tudinally in  order  that  they  may  give  warning 
by  leakage  if  fractured. 

58.  The  Relative  Strength  of  Shell  and 
FIG.  68.  "  Sectional  "  Boilers,  and  consequently,  in 

large  degree,  their  relative  safety,  "is  measured  by  the  relative 
magnitude  of  their  largest  parts.  As  remarked  by  John  Stevens, 


MATERIALS— STRENGTH  OF    THE   STRUCTURE.         149 

the  inventor,  the  sectional  boiler,  with  its  smaller  members  and 
subdivided  steam  and  water  chambers,  is  safe  in  proportion  as 
the  sizes  of  the  latter  are  diminished  ;  while  the  large  shells  of 
the  common  forms  of  boiler  are  liable  to  dangerous  rupture  in 
proportion  as  their  diameters  are  increased.  The  strengths  of 
cylindrical  reservoirs  subjected  to  internal  pressure,  as  are  the 
shells,  steam-drums,  and  mud-drums  of  shell  boilers,  and  the 
tubes  and  steam-reservoirs  of  sectional  boilers,  are  subject  to 
laws  so  simple,  and  are  computed  by  methods  of  such  easy  ap- 
plication, that  there  never  need  be  any  doubt  in  regard  to  the 
margin  of  safety  existing  in  either  case  when  new.  Flues  and 
old  boiler-shells  are  less  amenable  to  calculation,  and  are  thus 
more  unsafe.  Water-tubular  boilers  are  comparatively  safe 
under  all  conditions  of  ordinary  operation,  and,  when  compared 
with  the  other  type  of  steam-generator,  are  vastly  safer. 

59.  A  Loss  of  Strength  and  of  Ductility  is  very  often  ob- 
served in  the  iron  of  which  boilers  are  composed,  as  they  ad- 
vance in  age,  due  to  the  progress  of  oxidation,  probably,  within 
and  between  the  laminae  of  which  the  sheets  may  be  composed. 
The  plate  may  be  thus  very  nearly  destroyed,  at  times,  before 
this  action  may  be  detected.  In  some  cases  the  iron  may  be 
nearly  all  destroyed,  and  only  a  sheet  of  oxide  may  remain  ; 
while  the  boiler,  if  not  working  under  high  pressure,  may  still 
appear  sound.  Such  deterioration  is  often  a  source  of  great 
danger. 

Excessively  high  temperature  not  infrequently  gives  rise  to 
a  loss  of  tenacity  of  serious  amount  with,  fortunately,  in  most 
cases,  increase  of  ductility.  This  is  not  invariably  the  case, 
however,  as,  at  a  "  black  heat  "  just  below  redness,  a  critical 
temperature  is  reached  at  which  the  iron  may  exhibit  great 
brittleness. 

The  physical  conditions  thus  modifying  strength  have  been 
already  described  at  considerable  length.  These  changes  occur 
in  steam-boilers  through  the  action  of  a  variety  of  special 
causes.  Ordinary  oxidation,  general  and  local,  especially  when 
accelerated  by  voltaic  action,  produces  in  many  cases  rapid  de- 
terioration ;  the  constant  and  often  great  changes  of  tempera- 
ture due  to  not  only  the  ordinary  working  of  the  boiler,  but  also 


THE   STEAM-BOILER. 

at  times  to  overheating  of  parts  exposed  to  flame,  may  produce 
still  more  formidable  effects  ;  and  even  the  continual  changing 
of  form  caused  by  variations  both  of  pressure  and  temperature, 
after  the  lapse  of  considerable  periods  of  time,  may  give  rise  to 
important  losses  of  ductility,  and  sometimes  of  strength.  Steel 
is  especially  liable,  if  too  hard,  to  loss  of  quality  and  danger- 
ous injury  by  cracking,  in  consequence  of  such  action. 

60.  The  Deterioration  of  Boilers  with  age  and  with  use 
is  in  nearly  all  cases  due  to  modification  of  quality  of  metal,, 
and  to  reduction  of  section  of  parts  exposed  to  stress  and 
strain.  This  deterioration  is  certain  to  occur  to  a  greater  or 
less  extent ;  but  its  rate  is  usually  indeterminate,  and  it  conse- 
quently happens  that,  except  by  actual  inspection  and  test,  it 
is  impossible  to  know,  at  any  time  after  a  boiler  is  built  and 
set  in  operation,  just  what  is  its  strength  and  whether  it  is  safe. 

This  deterioration  may  be  to  a  certain  extent  controlled 
and  retarded  by  care  and  by  the  adoption  of  proper  precau- 
tions. The  principal  requisite  is  the  keeping  of  every  part  dry, 
and  at  a  temperature  below  that  of  "  burning"  or  rapid  oxi- 
dation. Loss  of  strength,  elasticity,  ductility,  and  resilience 
will,  however,  always  take  place ;  and  the  boiler,  whether  in  use 
or  not,  should  always  be  very  carefully  examined  at  such  inter- 
vals as  shall  insure  its  condition  being  known  at  all  times,  and 
such  as  shall  secure  a  safe  adjustment  of  the  pressure  main- 
tained within  it  to  its  reduced  strength.  Every  element  and 
member  of  the  structure  will  inevitably  depreciate,  and  the 
most  insignificant  part  must  be  kept  under  proper  supervision 
to  insure  safe  operation. 

Experiment  has  shown  that  steel  boiler-plate,  exposed  to 
repeated  heating  to  high  temperatures,  and  cooling  down  again, 
loses  less  by  oxidation  than  does  iron,*  and  retains  its  quality 
better.  Steel  loses  rather  more  than  iron  when  exposed  to  the 
action  of  sea-water,  f  and  should  never,  if  it  can  be  conveniently 
avoided,  be  placed  under  such  circumstances  in  contact  with 
iron.  Its  own  scale  also  produces  an  acceleration  of  galvanic 


*  Engineering,  April  20,  1883. 

•)•  Trans.  Inst.  Naval  Architects,  vol.  xxiii.  p.  143. 


MATERIALS— STRENGTH  OF   THE   STRUCTURE.         l$l 

action,  and  it  is  best,  where  practicable,  to  remove  all  the  scale 
by  "  pickling"  in  dilute  hydrochloric  acid  or  in  sal  ammoniac. 

61.  Inspection  and  Test  of  boilers,  at  regular  intervals  and 
by  methods  that  are  thoroughly  reliable,  is  now  universally  rec- 
ognized as  not  only  essential  to  permanent  safe  use  of  steam- 
generators,  but  also  as  necessary  to  secure  maximum  efficiency 
in  their  operation. 

Such  examinations  and  tests  are  usually  made  by  expert  in- 
spectors who  make  a  business  of  that  work,  and  who  have  thus 
acquired  exceptional,  sometimes  most  extraordinary,  skill  in  the 
detection  of  injury  and  its  cause.  The  methods  pursued  and 
the  rules  adopted  will  be  given  later,  in  chapters  devoted  to 
the  description  of  the  methods  of  construction  and  to  the  pre- 
scription of  forms  of  specification  and  contracts,  and  of  the  re- 
quisites of  full  conformance  with  the  latter. 


CHAPTER   III. 

THE   FUELS   AND   THEIR   COMBUSTION. 

62.  The  Chemical  and  Physical  Principles  involved  in 
the  combustion  of  fuel,  the  development  of  heat  and  its  trans- 
fer, are  all  well  known  and  capable  of  very  definite  expression. 

Combustion  may  be  defined  as  the  rapid  combination  of  any 
oxidizable  substance  with  oxygen.  The  result  of  such  combi- 
nation is  the  production  of  new  compounds  of  definite  charac- 
ter, and  in  quantities  readily  calculable  when  the  amount  of 
each  of  the  combustible  constituents  is  given.  It  is  also  known, 
very  precisely,  how  much  heat  is  produced  by  the  combustion 
of  any  given  weight  of  any  one  of  the  more  familiar  combusti- 
bles, and  how  much  of  that  heat  is  available  for  transfer  to  a 
steam-boiler  or  other  apparatus  of  utilization,  when  the  com- 
bustion is  complete  and  perfect. 

Perfect  combustion  occurs  when  all  of  the  combustible  is 
burned,  and  with  the  result  of  producing  the  highest  stage  of 
oxidation.  Carbon  is  perfectly  burned  when  it  is  wholly  con- 
verted into  carbon  dioxide  and  carbonic  acid.  Wood,  or  other 
fuel  containing  hydrogen,  is  perfectly  consumed  when  all  its 
carbon  is  oxidized  to  carbonic  acid,  and  all  its  hydrogen  is 
united  with  oxygen  to  form  steam. 

Chemical  combination  invariably  produces  heat,  and  de- 
composition as  inevitably  results  in  the  absorption  of  heat  in 
precisely  the  amount  due  to  the  opposite  process.  If  both 
combination  and  decomposition  take  place  in  complex  chemi- 
cal changes,  the  heat  produced  is  the  net  result  of  both  actions. 

Several  interesting  and  important  principles  are  recognized 
by  writers  on  this  general  subject,  as  controlling  the  develop- 
ment of  heat  by  combustion.  Berthelot  first  called  attention 
to  the  fact  that  the  total  heat  evolved  in  any  case  of  chemical 


THE  FUELS  AND    THEIR   COMBUSTION.  153 

combustion  is  a  measure  of  the  energy  expended  in  the  separa- 
tion of  the  resulting  compound  into  its  elements.  The  same 
chemist  announced  a  second  law,  also  known  by  his  name : 
The  quantity  of  heat-energy  evolved  or  absorbed  in  any  chemi- 
cal change  of  this  kind,  where  no  mechanical  work  is  done,  is 
dependent  purely  on  the  initial  and  final  states,  and  not  at  all 
on  the  intermediate  process  of  change.  Thus  the  heat  pro- 
duced in  a  furnace  depends  on  the  final  product  of  combustion, 
and  not  at  all  on  whether  the  carbon,  for  example,  has  been, 
at  intermediate  stages,  wholly  or  partly  burned,  and  has  existed 
in  greater  or  less  proportion  in  the  state  of  carbon  monoxide 
or  of  carbon  dioxide.  Berthelot's  third  law  asserts  that  in  any 
chemical  action  the  tendency  is  toward  that  method  of  change 
which  will  yield  the  greatest  amount  of  heat.  In  other  words, 
the  tendency  always  exists  to  produce  complete  transformation 
of  potential  into  actual  energy. 

63.  The  Fuels  used  in  Engineering*  are  anthracite  and 
bituminous  coals,  coke,  wood,  charcoal,  peat,  and  combustible 
gases  obtained  by  the  distillation  of  the  solid  kinds  of  fuel.  The 
oils — animal,  vegetable,  and  mineral — and  the  solid  hydrocar- 
bons, of  which  bitumen  is  a  type,  are  occasionally  used  also. 
All  consist  of  either  pure  carbon  or  of  combinations  of  carbon, 
hydrogen,  and  non-combustible  substances.  The  mineral  oils 
and  liquid  fuels  generally  promise  excellent  results  when  satis- 
factory methods  shall  have  been  found  to  secure  the  conditions 
of  perfect  combustion.  In  making  a  selection  of  a  fuel  the 
engineer  is  aided  greatly  by  a  knowledge  of  the  origin  and 
general  characteristics  of  those  combustibles  from  which  he 
may  be  called  upon  to  select  the  one  best  adapted  to  any  given 
case. 

Each  form  of  fuel,  solid,  liquid,  and  gaseous,  is  specially 
adapted  to  particular  purposes ;  and  in  selection  the  engineer 
and  metallurgist  should  carefully  examine  all  of  the  circum- 
stances of  the  case  under  consideration,  in  order  to  determine 
from  which  of  these  classes  the  fuel  required  should  be  selected  ; 


*  Adapted  largely  from  the  Author's  "The  Materials  of  Engineering,"  vol.  i. 
N.  Y.  :  J.  Wiley  &  Sons,  1885. 


154 


THE   STEAM-BOILER. 


and,  this  choice  having  been  made,  he  will  next  select  that 
quality  which  best  fulfils  the  requirements  of  the  case. 

COMPOSITION  OF  COMBUSTIBLES,  CARBON  TAKEN  AS  100. 


Carbon. 

Hydrogen. 

Oxygen. 

Wood      .      ...    

IOO 

12   4.8 

8q   O7 

Peat   

IOO 

Q  8q 

ec    67 

Lignite                                       . 

IOO 

8    17 

42    42 

Bituminous  Coal      .  .               . 

IOO 

6    12 

21    23 

Anthracite  Coal  

IOO 

2    84. 

I    74. 

Coal,  whether  anthracite  or  bituminous,  is  a  fossil  of  vege- 
table origin.  It  is  always  associated  with  some  earthy  matter, 
and  the  latter  is  sometimes  present  in  such  quantities  as  to 
destroy  the  value  of  the  coal  as  a  fuel. 

Coal  is  sometimes  found  so  slightly  altered  as  to  differ  but 
little  in  chemical  composition  and  in  physical  structure  from 
recent  vegetable  substances ;  and  in  other  cases  it  is  so 
thoroughly  changed  as  to  have  become,  in  all  but  its  chemical 
constitution,  a  mineral.  Some  of  the  more  completely  fossilized 
bituminous  coal  breaks  into  cubic  and  rhomboidal  fragments,, 
but  the  anthracite  exhibits  little  or  no  traces  of  crystallization. 

Chemical  examination  shows  coal,  as  already  indicated,  to 
be  composed  of  both  organic  and  inorganic  matter.  The  for- 
mer is  purely  vegetable,  and  the  latter  consists  of  earthy  mat- 
ter above  which  the  ligneous  portions  once  grew. 

Destructive  distillation  resolves  the  organic  matter  into  its 
invariable  ultimate  constituents,  carbon,  hydrogen,  and  oxygen,, 
which  come  from  the  retort  as  solid  carbon,  or  coke,  liquid  tar,, 
gaseous  ammonia,  benzole,  naphtha,  paraffine,  illuminating  gas, 
sulphurous  acid,  and  other  substances,  in  various  proportions. 
The  inorganic  portion  is  left  as  an  ash  when  the  fuel  is  burned. 
It  consists  usually  of  silicates  in  varying  proportions. 

The  various  fossil  fuels  having  had  a  common  origin,  and 
being  all  more  or  less  decomposed  and  mechanically  altered 
vegetable  matter,  are  found  to  exist  in  all  states  intermediate 
between  that  of  recent  vegetation  and  that  of  completely 
mineralized  graphitic  anthracite. 


THE  FUELS  AND    THEIR   COMBUSTION. 


155 


Their  classification  is  therefore  an  arbitrary  one,  and  it  fre- 
quently happens  that  a  particular  species  of  coal  lies  so  exactly 
between  two  classes  as  to  make  it  difficult  to  determine  to 
which  it  should  be  assigned. 

The  anthracites  are  found  among  the  older  carboniferous 
strata;  the  bituminous  coals  come  from  the  secondary,  and  the 
softest  and  least  altered  varieties  from  the  tertiary,  formations. 

The  following,  representing  approximately  the  gradual 
change  of  composition  as  fossilization  affects  the  alteration  of 
woody  fibre,  is  given  by  Dr.  Wagner: 

CHANGE   OF  COMPOSITION  OF   FOSSIL  FUELS. 


Carbon. 

Hydrogen. 

Oxygen. 

Cellulose     .        .         ... 

C2    6* 

e    2^ 

42  10 

Peat     

60  44 

*    06 

qo    60 

66.06 

5  -  27 

27.  76 

"       (earthy  brown  coal).  .  .  . 
Coal  (secondary)  

74.20 
76  18 

5-89 
*  64 

I9.QO 

18  07 

QO.  ZO 

c    (X 

4  .40 

Anthracite     .  .       .         .  . 

Q2      8^ 

*  06 

3IQ 

In  the  above  analyses  earthy  matter  is  excluded. 

64.  Anthracite  Coal,  called  sometimes^/^;?^,  and  sometimes 
blind  or  stone  coal,  consists  of  carbon  and  inorganic  substances, 
and  is  usually  free  from  hydrocarbons.  Some  varieties  are 
thoroughly  mineralized  and  have  become  graphitic.  The  or- 
dinary varieties  of  good  anthracite  are  hard,  compact,  lustrous, 
and  sometimes  iridescent.  The  color  is  intermediate  between 
jet  black  and  that  of  plumbago. 

It  is  amorphous  and  somewhat  vitreous  in  structure,  the 
hardest  varieties  falling  to  pieces  when  suddenly  heated,  and 
sometimes  breaking  up  into  very  small  fragments,  thus  caus- 
ing considerable  loss  even  when  carefully  "fired."  It  some- 
times gives  out  a  ringing  sound  when  struck.  It  is  a  strong, 
dense  coal,  its  specific  gravity  ranging  from  1.4  to  1.6.  It  has  a 
high  colorific  value. 

It  burns  without  smoke  and  without  flame  unless  containing 
moisture,  the  vapor  of  which  produces  a  yellow  flame  of  com- 
paratively low  temperature.  It  kindles  slowly  and  with  dif- 


THE   STEAM-BOILER. 

ficulty;  and,  once  kindled,  requires  to  be  carefully  and  skilfully 
managed  to  secure  economic  efficiency. 

A  representative  variety  has  a  specific  gravity  1.55,  and  con- 
tains, exclusive  of  ash,  carbon,  94  per  cent,  hydrogen  and  oxygen 
(moisture)  6  per  cent.  Of  the  latter,  2-J  per  cent  is  hygroscopic, 
but  is  held  with  great  tenacity. 

The  percentage  of  ash  varies  greatly,  even  in  the  same  variety, 
and  in  specimens  from  the  same  bed.  It  may  be  estimated,  as 
an  average,  at  above  ten  per  cent,  while  the  total  loss  in  ash, 
fine  coal,  and  clinker  will  be  likely  sometimes  to  reach  double 
that  proportion  in  ordinary  furnaces.  When  selecting  anthracite 
it  is  necessary  to  keep  this  fact  carefully  in  mind.  Twenty-four 
samples  of  anthracite  from  Pennsylvania,  analyzed  by  Britton, 
gave  as  a  mean — 

Carbon 9J-O5 

Volatile  matter 3.45 

Moisture 1.34 

Ash c 4  16 


100.00 


There  was  included  in  the  above,  sulphur  0.240,  phosphorus 
0.013. 

A  variety  of  this  class  of  coals,  similar  in  composition,  but 
differing  from  the  typical  anthracite  above  described  in  struc- 
ture, has  been  sometimes  called  semi-anthracite. 

It  does  not  exhibit  the  conchoidal  fracture  of  the  latter,  but 
is  somewhat  lamellar,  and  is  marked  by  fine  joints  or  planes  of 
cleavage.  It  crumbles  readily,  and  has  less  density  than  the 
preceding. 

One  method  of  distinguishing  good  examples  of  the  two 
varieties  is  found  in  the  fact  that  the  latter,  when  just  fractured, 
soils  the  hand,  while  the  former  does  not.  The  latter  variety 
kindles  quite  readily  and  burns  freely. 

An  example  of  this  coal  contained,  in  one  hundred  parts, 
carbon,  90;  hydrogen  and  oxygen,  1.5  ;  ash,  8.5. 

65.  The  Bituminous  Coals  are  sometimes  divided  into 
three  classes. 

Dry  bituminous  coal  contains  about  75  per  cent  of  carbon, 


THE  FUELS  AND    THEIR    COMBUSTION.  !$/ 

5  per  cent  hydrogen,  and  4  per  cent  oxygen.  That  part  of  the 
hydrogen  which  is  combined  with  carbon  is  capable  of  adding 
to  the  heat-giving  power  of  the  coal.  This  coal  is  lighter  than 
anthracite,  its  specific  gravity  being  about  1.3.  Its  color  is 
black  or  nearly  black,  and  its  lustre  resinous ;  it  is  moderately 
hard,  and  burns  freely.  Its  structure  is  weak,  brittle  and  splin- 
tery, fine-grained,  and  of  uneven  surface.  It  kindles  with  less 
difficulty  than  any  variety  of  anthracite,  but  less  readily  than 
the  bituminous  coal  to  be  described.  It  burns  with  a  moderate 
flame,  and  gives  off  little  or  no  smoke. 

Bituminous  caking  coal  contains  sometimes  as  little  as  60  per 
cent  of  free  carbon,  and  the  maximum  proportion  is,  perhaps, 
70  per  cent.  It  contains  5  or  6  per  cent  each  of  oxygen  and 
hydrogen,  and  the  remaining  portion,  amounting  sometimes  to 
30  per  cent,  is  incombustible.  Its  specific  gravity  is  about  1.25. 
It  is  moderately  compact ;  its  fracture  is  uneven,  but  not  splin- 
tery; its  color  is  a  less  decided  black  than  the  preceding,  and 
its  lustre  is  more  resinous.  When  heated  it  breaks  into  small 
fragments  if  the  proportion  of  bitumen  is  insufficient  to  cause  it 
to  cohere  before  becoming  thoroughly  softened,  but  afterward, 
as  it  becomes  more  highly  heated,  the  pieces  become  pasty  and 
adherent,  and  the  whole  mass  becomes  compact  and  hard  as  the 
gaseous  constituents  are  expelled  by  heat. 

This  coal,  ignited  in  air,  burns  with  a  yellowish  flame  and 
very  irregularly  unless  kept  continually  stirred  to  prevent  ag- 
glomeration and  consequent  checking  of  the  draught.  It  can- 
not be  successfully  used,  therefore,  when  great  heat  is  required. 
It  is  valuable  for  the  manufacturer  of  gas  and  of  coke,  and  can 
be  used  in  small  grates  where  but  moderate  heat  is  obtained. 

Long  flaming  bituminous  coal  is  quite  similar  to  the  pre- 
ceding, differing  chemically  in  composition  and  containing  a 
larger  proportion  of  oxygen.  It  burns  with  a  long  flame,  and  has 
a  strong  tendency  to  produce  smoke.  Some  varieties  cake  like 
the  preceding,  others  do  not ;  but  all  ignite  readily  and  burn 
freely,  consuming  rapidly. 

There  are  many  varieties  of  coal  in  each  of  the  above- 
named  classes,  the  gradation  being  sometimes  marked  and 
sometimes  barely  distinguishable. 


153  THE   STEAM-BOILER. 

American  anthracites  have  been  found,  by  experiments 
made  under  the  direction  of  the  United  States  Navy  Depart- 
ment, to  have  a  mean  evaporative  efficiency,  in  marine  boilers, 
of  8.9  pounds  of  water  evaporated  from  212°  Fahr.  (100°  Cent.) 
per  pound  of  coal.  The  bituminous  coals  of  the  United  States 
were  found  to  evaporate  an  average  of  9.9  pounds  of  water  per 
pound  of  fuel,  under  similar  conditions.  The  average  efficiency 
of  British  coals  is  given  by  Bourne  at  about  8.7.  American 
anthracites  evaporated  10.69  pounds  of  water  per  pound  of 
combustible  matter  contained  in  the  fuels,  and  the  bituminous 
coals  10.84,  from  212°  Fahr.* 

These  results  are  practically  identical  for  the  two  kinds  of 
coal ;  but  the  average  of  the  best  known  varieties  gives  a  dif- 
ference which  is,  with  such  good  varieties,  in  favor  of  anthra- 
cite. 

66.  Lignite,  or  Brown  Coal,  is  of  more  recent  and  of  more  in- 
complete formation  than  the  bituminous  coals,  and  occupies  a 
position  intermediate  between  the  true  coals  and  peat.  It  con- 
tains from  30  to  60  per  cent  of  carbon,  5  to  8  per  cent  of 
hydrogen,  and  20  to  25  per  cent  of  oxygen.  It  is  very  light 
when  pure,  having,  according  to  Regnault,  a  specific  gravity  of 
from  i.io  to  1.25.  The  heavier  varieties  contain  much  compact 
earthy  matter. 

Lignite  is  found  in  tertiary  geological  formations.  It  is 
brown  in  color,  has  the  woody  structure  well  denned,  and  is 
usually  lustreless.  Where  it  approaches  the  bituminous  coals 
in  age,  it  also  approximates  to  them  in  structure  and  other 
characteristics.  It  frequently  contains  considerable  moisture, 
which  can  only  be  removed  by  high  temperature  or  by  long 
seasoning,  and  the  lignite,  once  dried,  must  be  carefully  pre- 
served in  dry  situations  if  not  used  at  once,  as  it  reabsorbs 
moisture  with  great  avidity. 

When  thoroughly  dry  it  kindles  readily,  burns  freely,  and 
is  consumed  rapidly.  It  is  not  usually  considered  a  valuable 
kind  of  fuel.  It  occupies  considerably  more  space  weight  for 
weight  than  the  true  coals,  burns  as  an  average  a  third  more 


*See  American  Institute  Reports:  Tests  of  Steam  Boilers,  1874. 


FUELS  AND    THEIR   COMBUSTION.  159 

rapidly,  and  its  evaporation  of  water  per  pound  of  fuel  is  about 
25  per  cent  less.  To  obtain  maximum  evaporative  efficiency  a 
slow  rate  of  combustion  is  found  most  effective. 

67.  Peat,  sometimes  called  Turf,  is  obtained  from  bogs  and 
swampy   places.     It    consists   of    the    interlaced    and    slightly 
decayed  roots  of  vegetation,  which,  although  buried  under  a 
superincumbent  mass  of  similar  material  and  mingled  with  some 
earthy   matter,  retains    its    ligneous  structure    and    nearly   all 
the    chemical    characteristics    of    unaltered    vegetable    matter. 
Submitted  to  the  great  pressure  and  the  warmth  which  have 
for   ages   acted    upon    the    coal-beds,  it    would    also   probably 
become  coal. 

Dried  in  the  air,  it,  like  the  lignites,  retains  moisture  per- 
sistently, and  is  usually  found  to  contain  30  per  cent  after 
drying.  After  completely  removing  all  water,  an  average 
specimen  would  contain  about  60  per  cent  of  carbon,  5  to  10 
per  cent  hydrogen,  and  30  or  40  per  cent  of  oxygen.  The  ash 
varies  very  greatly,  sometimes  being  as  little  as  5,  and  in  other 
•cases  as  high  as  25  per  cent. 

A  pound  of  wood  charcoal  has  nearly  the  same  value  as  a 
fuel  as  1.66  pounds  of  peat  of  average  quality. 

Peat  is  frequently  used  in  large  quantities  for  heating  pur- 
poses, and  attempts  have  been  made,  with  encouraging  results, 
to  use  it  in  metallurgical  operations. 

When  to  be  thus  used,  it  is  cut  from  the  bog  with  sharp 
spades,  ground  up  in  a  machine  specially  designed  for  the 
purpose,  and  dried  by  spreading  it  where  it  can  have  full 
exposure  to  the  sun  and  air. 

It  is  frequently  compressed  by  machinery  until  its  density 
approaches  that  of  the  lighter  coals,  and  it  is  used  in  blocks 
of  such  size  as  are  found  best  suited  to  the  particular  purpose 
for  which  it  is  prepared. 

Its  charcoal  makes  excellent  fuel  for  use  in  working  steel 
and  welding  iron.  It  is  frequently  found  to  be  a  very  excel- 
lent fuel  for  other  purposes,  and  is  extensively  used  in  some 
localities.  Its  specific  gravity  is  usually  about  0.5. 

68.  ^A/ood,  thoroughly  seasoned,  still  contains  about  20  per 
cent  of  moisture. 


160  THE   STEAM-BOILER. 

The  moisture  being  completely  driven  off  by  high  tem- 
perature, there  is  left  about  50  per  cent  carbon,  and  combined 
oxygen  and  hydrogen  compose  the  remainder,  in  very  nearly 
the  proportions  which  form  water.  The  pines  and  firs  contain 
turpentine,  and  other  woods  contain  frequently  a  minute  pro- 
portion of  hydrocarbons  peculiar  to  themselves. 

The  proportion  of  ash  varies*  from  about  0.5  per  cent  to  5 
per  cent.  The  woods  all  evaporate  very  nearly  the  same  weight 
of  water  per  pound  of  fuel.  The  lighter  woods  take  fire  most 
readily  and  burn  most  rapidly;  the  denser  varieties  give  the 
most  steady  heat  and  burn  longest. 

Where  radiated  heat  is  desired  the  hard  woods  are  much  the 
most  efficient. 

The  seasoning  of  wood  has  been  described  in  that  part  of 
this  work  which  treats  of  timber. 

Thorough  seasoning  in  the  open  air  requires  from  six 
months  to  a  year,  and  is  the  only  method  generally  adopted 
for  wood  intended  to  be  used  as  fuel.  One  cord  of  hard  wood, 
such  as  is  used  on  the  Northern  lakes  of  the  United  States,  is 
said  to  be  equal  in  calorific  power  to  one  ton  of  anthracite  coal 
of  medium  quality.  One  cord  of  soft  wood,  such  as  is  used  by 
steamers  on  Western  rivers,  is  equal  in  heating  power  to  960 
pounds  (436  kilogrammes)  or  12  bushels  (423  cubic  decimetres) 
of  Pittsburg  coal.  One  cord  of  well-seasoned  yellow  pine  is 
equivalent  to  J  ton  (500  kilogrammes)  of  good  coal.  (See  §  84.) 

69.  Coke  is  made  from  bituminous  coal  by  subjecting  it  to 
such  high  temperature  as  to  deprive  it  of  its  volatile  con- 
stituents. 

The  presence  of  moisture  in  some  of  the  coals  largely 
reduces  their  heating  power.  The  bituminous  matter  causes 
them  to  fuse  and  to  form  a  coherent  mass,  and,  by  thus  pre- 
venting the  passage  of  air,  destroys  their  efficiency  for  many 
purposes.  The  presence  of  sulphur  and  of  deleterious  volatile 
substances  in  many  coals  also  precludes  their  application  to  the 
reduction  of  iron  ores,  and  destroys  their  value  for  other  metal- 
lurgical purposes.  All  of  these  volatile  materials  being  driven 
off  by  heat,  a  mass  of  fixed  carbon  containing  only  earthy 
impurities  remains,  which  "  coke "  constitutes  the  fuel  with 


THE  FUELS  AND    THEIR   COMBUSTION.  l6l 

which  some  of  the  most  extensive  and  important  metallurgical 
industries  are  conducted.  These  volatile  matters  are  sometimes 
utilized,  but  are  generally  wasted,  except  where  the  coke  is 
considered  a  secondary  product,  as  in  the  manufacture  of  illu- 
minating gas. 

Coking  is  carried  on  by  either  of  three  methods — in  open 
heaps,  in  coke  ovens,  or  in  retorts. 

The  first  method  is  extremely  wasteful,  and  is  rarely  prac- 
tised ;  the  second  is  more  economical ;  and  the  third  is  the  best 
where  gas  is  manufactured,  and  is  the  only  one  practised  in 
that  case.  The  second  method  is  that  generally  adopted  where 
the  coke  is  the  primary  product,  as,  although  not  as  economical 
as  the  last,  it  produces  a  strong  coke  which  is  much  better 
adapted  for  use  in  furnaces  than  that  afforded  by  the  last 
method,  which,  although  allowing  of  the  complete  separation 
and  collection  of  the  liquid  and  gaseous  products  of  distillationr 
yields  a  coke  which  has  too  little  density  and  strength  to  make 
it  a  valuable  fuel. 

Coak  made  in  ovens  is  usually  of  a  dark  gray  color,  porous, 
hard,  and  brittle.  The  best  gives  out  a  slight  ringing  sound 
when  struck,  and  has  something  of  the  metallic  lustre.  It 
makes  an  intense,  clear  fire,  and  it  should  riot  be  forced  so  as 
to  injure  either  the  boiler  or  the  grate  by  burning  the  iron. 
Where  the  coals  contain  sulphur  but  are  free  from  moisturef 
provision  should  be  made  for  the  passage  of  a  supply  of  steam 
through  the  oven.  This  will  give  up  its  oxygen  to  the  metal 
with  which  the  sulphur  is  combined,  and  the  hydrogen,  uniting 
with  the  latter,  forms  sulphuretted  hydrogen.  The  coke  is 
thus  left  comparatively  free  from  the  noxious  ingredient,  and 
as  this  is  usually  the  only  constituent  of  bituminous  coal  which 
injuriously  affects  iron,  the  coke  is  a  better  fuel  than  the  coal 
from  which  it  is  made. 

Various  coals  yield  from  33  per  cent  to  90  per  cent  of  their 
weight  in  coke.  The  latter  containing  all  the  ash,  the  percent- 
age of  ash  in  coke  will  be  higher  than  in  the  coal  from  which  it  is 
prepared.  Coke  has  a  strong  tendency  to  absorb  moisture,  and 
may,  when  unprotected  from  dampness,  condense  15  or  20  per 
cent  of  its  own  weight  within  its  pores, 
ii 


1 62  THE   STEAM-BOILER. 

Many  cokes  contain  15  percent  ash  and  I  or  even  2  per 
cent  sulphur;  while  others  contain  but  3  to  5  per  cent  ash  and 
TL  per  cent  sulphur. 

70.  Charcoal  has  the  same  relation  to  wood  that  coke  has 
to  bituminous  coals. 

It  is  made  from  all  kinds  of  wood,  hard-wood  charcoal 
being  the  best  for  fuel.  Wood  of  about  twenty  years  of  age  is 
preferred,  and  should  be  charred  before  decay  has  commenced. 
The  methods  of  preparation  are  substantially  the  same,  and  the 
chemical  constitution  of  the  product  is  very  similar,  although 
its  physical  characteristics  are  quite  different. 

Charcoal  prepared  by  charring  in  heaps  seldom  amounts  to 
more  than  20  per  cent  of  the  total  weight  of  wood  used ;  care- 
lessness in  conducting  the  process  may  reduce  the  weight  of 
product  far  below  even  that  figure.  A  considerable  loss  is 
unavoidable,  since  the  charring  of  one  portion  must  be  effected 
by  the  heat  obtained  from  the  combustion  of  another  part  of 
the  wood.  Sound  wood  is  selected,  cut  in  billets  four  or  five 
feet  in  length,  and,  when  large,  split  into  sticks  of  from  three 
to  six  inches  in  thickness.  It  is  best  to  assort  the  wrood, 
placing  each  kind  in  piles  by  itself.  In  making  up  the  heap 
the  ground  is  cleared,  a  stake  is  set  at  the  centre  of  the  cleared 
space,  and  a  layer  of  wood  is  put  down  with  all  the  sticks  laid 
radially,  and  the  interstices  filled  with  smaller  sticks.  On  this 
layer  the  rest  of  the  wood  is  piled  on  end,  beginning  by  leaning 
sticks  against  the  centre  stake.  The  whole  is  finally  covered 
with  another  closely  packed  layer,  which  in  turn  is  completely 
covered  with  sods. 

A  central  hole  is  left,  and  also  an  uncovered  ring  around  the 
base  five  or  six  inches  high,  for  the  air-supply.  One  or  two 
horizontal  passages  left  in  the  pile  conduct  the  gases  to  the 
centre,  where  they  rise,  passing  out  at  the  hole  made  by  pulling 
out  the  centre  stake  before  firing  the  pile. 

The  fire  being  started  and  actively  burning,  all  openings 
are  closed,  and  combustion  is  perfectly  controlled  by  altering 
their  number  and  position.  The  condition  of  the  fire  is  indi- 
cated by  the  color  of  the  smoke,  which  should  be  black  and 
thick ;  when  it  is  light  and  bluish  the  draft  should  be  more 


THE  FUELS  AND    THEIR    COMBUSTION.  163 

completely  checked.  The  work  is  finished  when  the  wood  at 
the  exterior  of  the  pile  is  found  charred.  All  openings  are 
then  closed,  and  the  fire  is  thus  extinguished.  The  pile  can 
be  usually  opened  on  the  following  day,  and  the  removal  of 
charcoal  begun.  So  crude  a  process  is  very  liable  to  excessive 
losses  from  the  difficulty  experienced  in  adjusting  the  supply 
of  air,  and  in  conducting  the  heated  products  of  combustion  to 
precisely  the  right  points,  and  in  precisely  the  right  proportions 
to  secure  maximum  efficiency. 

The  presence  of  moisture  in  wood  is  productive  of  loss 
by  giving  rise  to  the  formation  of  carbonic  oxide  and  of  new 
hydrocarbons.  They  carry  off  carbon  which  would  otherwise 
have  been  left  in  the  solid  state  as  so  much  charcoal. 

Dry  wood,  charred  in  a  retort,  yields  as  a  maximum  about 
30  per  cent  of  its  weight  in  charcoal.  Of  the  carbon  originally 
contained  in  wood,  therefore,  by  the  first  method  of  charring 
not  above  one  half  may  be  expected  to  be  obtained  as  charcoal, 
while  by  the  last  method  three  quarters  may  be  obtained  by 
skilful  management.  The  latter  process  requires  the  expen- 
diture of  about  one  eighth  of  the  weight  of  wood  charred  for 
the  production  of  the  heat  demanded  by  that  process.  It 
therefore  yields  a  net  amount  in  charcoal  of  about  30  per 
cent  of  the  total  weight  of  wood  used.  The  wood  which  is 
used  for  fuel,  however,  may  be  of  less  value  than  that  charged 
into  the  retort.  Peat  charcoal  is  sometimes  made  by  similar 
methods,  but  is  little  used. 

Wood  heated  to  300°  Fahr.  (150°  Cent.)  for  a  considerable 
length  of  time  loses  60  per  cent  or  more  of  its  weight.  If 
heated  only  to  slightly  above  212°  Fahr.  (100  Cent.),  the  loss 
is  but  from  50  to  55  per  cent.  The  residue  resembles  charcoal, 
but  in  each  case  it  retains  some  volatile  matter  which  may  be 
driven  off  by  higher  temperatures.  Karsten  found  that,  by 
rapid  charring  at  high  temperatures,  he  obtained  as  an  average 
about  15  per  cent  charcoal  in  one  series  of  experiments;  while 
by  slowly  charring  the  same  woods  at  a  low  temperature  the 
percentage  obtained  averaged  about  25  per  cent. 

The  combustibility  of  cJiarcoal  is  greater  when  prepared  at  a 
low  than  when  prepared  at  a  high  temperature. 


164  THE    STEAM-BOILER. 

Good  charcoal  is  black,  with  a  high  lustre,  and  has  a  con- 
choidal  fracture.  It  is  quite  strong,  and  the  best  qualities  ring 
when  struck,  although  less  than  good  coke.  It  burns  without 
flame  or  smoke,  and  radiates  heat  strongly.  It  should  not  soil 
the  hands. 

Charcoal  and  coke  both  make  an  intense,  clear  fire,  and  with 
a  forced  draught,  giving  a  small  air-supply,  afford  an  extremely 
high  temperature,  which  is  liable  to  injure  the  grates  or  anything 
metallic  which  may  be  subjected  to  its  action. 

71.  Pulverized  Fuel,  or  Dust-fuel,  is  sometimes  used  in 
special  processes.  In  the  use  of  this  form  of  fuel  special  ar- 
rangements become  necessary  to  secure  thorough  intermixture 
of  the  fuel  with  the  supporter  of  combustion,  in  order  to  effect 
complete  oxidation.  The  fuel  itself  is  sometimes  prepared  by 
pulverizing  coal  or  other  combustibles;  and  sometimes  it  is 
obtained  from  the  large  deposits  of  "slack,"  "breeze,"  or  coal 
dust  which  are  found  wherever  coal  in  large  quantities  is  sub- 
jected to  attrition.  It  is  sometimes  burned  on  a  very  fine  grate, 
the  requisite  supply  of  air  being  secured  by  the  use  of  a  blast 
beneath  the  grate. 

One  of  the  most  successful  methods  is  that  pursued  by 
Whelpley  and  Storer,  and  by  Crampton.  In  this  process  a 
stream  of  mingled  dust-fuel  and  air  is  driven  into  the  furnace 
where  combustion  takes  place,  the  quantity  of  fuel  and  of  air 
being  capable  of  adjustment  in  such  a  manner  as  to  secure  the 
most  perfect  combustion.  This  method  has  been  applied  suc- 
cessfully, not  only  in  the  production  of  heat  simply,  but  also  in 
the  reduction  of  metals  from  their  ores.  The  facility  with 
which  an  oxidizing  or  a  reducing  flame  may  be  produced  at 
will  is  the  great  merit  of  the  process  in  the  latter  application. 
Its  advantage  for  heating  purposes  lies  in  the  power  which  it 
gives  of  utilizing  a  fuel  which  would  have  otherwise  no  value. 
In  making  "  muck-bar,"  an  economy  over  that  attained  with 
coal  of  above  20  per  cent  has  been  reported  to  have  been 
effected  by  the  use  of  this  process  and  fuel.  The  saving 
occurred  in  reduction  of  waste  of  metal,  as  well  as  in  simple 
economy  of  fuel.  At  the  United  States  Armory  at  Springfield, 
Massachusetts,  6.6  pounds  or  kilogrammes  of  fuel  were  con- 


7 HE   FUELS  AND    THEIR   COMBUSTION  165 

sumed  per  pound  or  kilogramme  of  iron  heated  to  the  welding 
heat,  where  16  had  been  required  by  the  old  process.* 

72.  Liquid  Fuels  have  been  used  to  a  limited  extent.  The 
liquids  best  adapted  for  use  as  fuel  are  the  mineral  oils.  They 
yield  an  intense  heat ;  the  products  of  combustion,  as  well  as 
the  fuels  themselves,  are  comparatively  free  from  deleterious 
-elements,  and  the  temperatures  obtained  by  their  use  are 
generally  easily  regulated,  when  they  are  burned  in  manageable 
quantities.  Their  tendency  is  to  give  off  combustible  gases, 
which  may  cause  serious  explosions ;  and  this  fact,  but  especially 
the  difficulty  met  with  in  uniformly  distributing  the  oil,  and  in 
properly  supplying  it  with  air  for  its  combustion,  have  hitherto 
prevented  the  general  use  of  these  fuels,  even  where  their  com- 
paratively high  cost  would  not  be  a  serious  objection  to  their 
application. 

Crude  petroleum,  on  distillation,  breaks  up  into  a  large 
number  of  hydrocarbon  compounds,  having  boiling-points 
varying  from  32°  Fahr.  (o°  Cent.)  to  700°  Fahr.  (371°  Cent.),  as. 
given  by  Van  der  Weyde.  Its  density  is  variable,  but  usually 
about  45°  Beaume,  corresponding  to  a  specific  gravity  of  about 
O.8,  the  gallon  weighing  6.67  pounds,  and  the  litre  weighing  0.8 
kilogramme.  It  contains  by  analysis:  carbon,  84;  hydrogen, 
14;  oxygen,  2.  The  latent  heat  of  its  vapor  is  about  one  fifth 
that  of  steam,  and  its  volume  25  cubic  feet  to  the  gallon  of  oil, 
or  0.2  cubic  metre  per  litre. 

The  "creosote"  or  "dead  oil"  produced  in  gas-making  is 
sometimes  used  as  fuel.  In  experiments  on  board  the  British 
steamer  Retriever,  in  1868,  where  creosote  was  used  for  the 
generation  of  steam  by  what  is  called  the  Dorsett  system,  the 
evaporation  was  about  14  pounds  or  kilogrammes  of  water 
from  a  boiling-point  per  pound  or  kilogramme  of  liquid  fuel 
used,  or  nearly  double  the  average  obtained  where  coal  was  used 
in  the  same  boiler. 

Dr.  Paul,  reporting  these  results,  gives  the  theoretic  evapo- 
rative power  of  the  constituents  of  this  fuel,  in  units  in  weight 
of  water  per  unit  of  fuel,  as  follows:  phenol,  12.25;  cressol, 

*  Report,  Lieut.  H.  Metcalf  to  Major  Burton,  Oct.  3ist,  1873. 


1 66  THE   STEAM-BOILER. 

13.01;  napthaline,  15.46;  xylol,  16.59;  cumol,  16.78;  cymol, 
16.94. 

Capt.  Selwyn,  R.  N.,  reported  an  evaporative  power  from 
boiling-point  of  16.77  parts  water  per  part  by  weight  of  a 
liquid  fuel  which  had  a  theoretical  efficiency  of  17.52  parts. 
In  another  instance  he  gives  the  evaporation  of  14.98  from 
the  boiling-point,  by  a  fuel  having  a  theoretical  evaporative 
power  of  17.5.  Deville  found  oil  from  Oil  Creek,  Pennsylva- 
nia, to  have  a  calorific  value  of  10,000  "calories,"  equivalent  to 
the  evaporation  of  16.17  parts  of  water  for  one  part  by  weight 
of  oil.  Of  this  13^  per  cent  was  lost  by  the  chimney,  and  by 
conduction  and  radiation.  Some  other  oils  give  slightly  higher 
figures. 

Liquid  fuels  have  probably  had  most  genera!  and  success- 
ful application  in  Russia,  where  Mr.  Urquehart  and  others 
have  adopted  it  for  locomotives,  and  many  steamers  in  South- 
ern Russia  have  been  fitted  with  petroleum  furnaces.  In  these 
cases  crude  petroleum  and  refuse  is  injected  into  the  furnace 
by  means  of  a  steam-jet  in  which  highly-superheated  steam  is 
employed.  The  furnace  is  lined  with  fire-brick  and  the  com- 
bustion-chamber as  well,  the  burning  jets  passing  first  through 
the  latter,  then  onward  to  the  furnace,  where  combustion  is 
completed.  The  brickwork  serves  as  a  reservoir  of  heat,  regu- 
lating the  supply,  and  also  at  times  re-igniting  the  jets  of  oil- 
spray  when  they  have  been  for  a  short  time  extinguished. 

The  use  of  oil  on  the  steamers  of  the  Central  Pacific  Rail- 
way Co.  gave  in  1884  an  economy  of  from  5  to  12  per  cent  in 
total  running  expense  as  compared  with  coal,  with  great  saving 
of  boilers  also. 

Experiments  made  by  Engineer-in-Chief  B.  F.  Isherwood, 
U.  S.  N.,  under  the  direction  of  the  U.  S.  Navy  Department, 
upon  various  systems  of  utilization  of  petroleum  as  a  fuel, 
gave  a  maximum  economy  over  the  use  of  anthracite  of  68 
per  cent  by  Fisher's  method  of  burning  oil,  and  38  per  cent 
by  Foote's  process  of  burning  liquid  and  solid  fuel  together ; 
he  reports  the  failure  of  another  method,  in  consequence  of 
the  obstruction  of  the  tubes  by  deposition  of  solid  carbon. 

Isherwood  states  the  advantages  attending  the  use  of  the 


THE  FUELS  AND    THEIR   COMBUSTION.  l6/ 

mineral  oils,  which  were  the  subject  of  his  experiments,  as  fol- 
lows : 

1.  A  reduction  of  weight  of  fuel  amounting  to  40^-  per  cent, 

2.  A  reduction  in  bulk  of  36^  per  cent. 

3.  A  reduction  in  the  number  of  firemen  ("  stokers")  in  the 
proportion  of  4  to  I. 

4.  Prompt  kindling  of  fires,  and   consequently  the   early 
attainment  of  the  maximum  temperature  of  furnaces. 

5.  The  fire  can  at  any  moment  be  instantaneously  extin- 
guished. 

Other  advantages,  unmentioned  by  him,  are  the  uniformity 
of  combustion  and  heating  attainable,  and  the  small  propor- 
tion of  ash.  The  disadvantages  are  given  as  follows : 

1.  Danger  of  explosions  occurring  by  the  taking  fire  of 
the  vapors  which  are  liable  to  arise   from  the  fuel,   and  to 
escape  from  the  tanks. 

2.  Loss  of  fuel  by  evaporation. 

3.  The  unpleasant  odors  which  distinguish  these  vapors. 

4.  The  comparatively  high   price,  which   price  would   be 
rapidly  augmented  by  any  general   introduction  of  the  pro- 
posed application  of  the  oils.* 

73.  Gaseous  Fuels  are  used  with  marked  success  in  some 
branches  of  metallurgical  work,  as  well  as  in  the  generation  of 
heat  for  ordinary  purposes. 

The  advantages  possessed  by  gaseous  fuels  are : 

1.  Convenience  of  management  of  temperature. 

2.  Freedom   from   liability  to   injure  material  with  which 
the  products  of  combustion  may  come  in  contact,  and  conse- 
quently, also,  allowing  the  use  of  fuel  of  inferior  quality  as  a 
source  of  the  gas. 

3.  The  facility  with  which  thorough  combustion  may  be 
secured. 

4.  The  readiness  with  which  the  flame  may  be  given  either 
an  oxidizing  or  a  deoxidizing  character. 


*  This  may  be  questioned,  since  recent  explorations  of  oil  deposits,  especially 
of  the  United  States,  indicate  an  immense  supply — as  immeasurable  and  probably 
nearly  as  inexhaustible  as  the  coal-fields. 


1 68  THE   STEAM-BOILER. 

5.  In  many  cases  economy  in  expense  of  operation. 
The  disadvantages  are  : 

1.  Danger   of    explosions  when    carelessly   or    unskilfully 
handled. 

2.  Expense  of  plant. 

74.  Artificial  Fuels,  other  than  charcoal,  coke,  and  gases, 
are  occasionally  used  in  the  production  of  high  temperatures. 

They  are  prepared  principally  from  refuse  of  natural  fuels, 
which  has  but  little  value  in  its  usual  condition,  but  which,  by 
special  processes,  is  simply  mixed  with  a  small  proportion  of 
fuel  of  better  quality  or  of  more  manageable  form,  and  is 
compressed  by  machinery  into  conveniently  shaped  blocks, 
called  briquettes.  This  refuse  is  found  in  large  quantities  in 
the  neighborhood  of  coal-mines,  and  wherever  coal  is  handled 
in  considerable  quantities. 

The  total  loss  in  this  form  in  mining  and  transportation 
amounts  to  from  one  third  to  one  half.  It  is  called,  as  has 
been  before  stated,  slack-coal. 

In  the  manufacture  and  transportation  of  coke  and  of 
charcoal,  large  quantities  of  refuse,  called  "  breeze/'  accumu- 
late ;  which,  although  very  rich  in  combustible  matter,  can- 
not be  utilized  in.  the  condition  in  which  it  is  found,  except 
by  special  contrivances.  The  sawdust  which  accumulates 
about  saw-mills  is  another  variety  of  combustible  belonging 
to  the  same  class ;  as  is  also  spent  tan-bark,  from  tanneries, 
and  "  bagasse,"  or  refuse  crushed  sugar-cane. 

They  are  most  frequently  mixed  with  some  cohesive  and  at 
the  same  time  combustible  substance,  as  coal-tar.  In  districts 
abounding  in  mineral  hydrocarbons,  as  in  the  neighborhood 
of  the  Caspian  Sea,  it  has  long  been  customary  to  mix  them 
with  clay,  and  thus  to  form  a  coherent  and  manageable  fuel. 
The  Norwegians  have  also  long  practised  their  method  of 
utilizing  sawdust  by  mixing  it  with  clay  and  vegetable  tar, 
and  moulding  it  into  bricks  of  such  size  and  shape  as  to  be 
conveniently  handled,  and  at  the  same  time  to  burn  freely 
and  without  waste.  It  has  been  often  urged,  and  with  some 
reason  apparently,  that  for  many  purposes  a  fuel  made  by 
careful  mixture  of  dust-fuel  with  pitch  or  other  combustible 


THE  FUELS  AND    THEIR    COMBUSTION.  169 

cementing  material  is  preferable  to  ordinary  coal,  in  conse- 
quence of  the  greater  convenience  with  which  it  can  be  stowed 
and  handled. 

Another  method  of  utilizing  waste  fuels  consists  in  thor- 
oughly mixing,  by  grinding,  charcoal-dust  from  the  kilns  with 
charred  peat,  spent  tan-bark,  and  the  proper  proportion  of  tar 
or  pitch  to  make  a  pasty,  adhesive  mass.  This  is  moulded  by 
machinery  and  dried  in  the  open  air,  and  then  finally  baked 
in  closed  retorts  at  a  low  heat.  Dust-coal  and  pitch  have  been 
made  into  a  good  fuel  in  quite  a  similar  manner  to  that  just 
described. 

75.  The  Heating  Power  of  any  Fuel  is  determined  by 
calculating  its  total  heat  of  combustion.  This  quantity  is  the 
sum  of  the  amounts  of  heat  generated  by  the  combustion  of 
the  unoxidized  carbon  and  hydrogen  contained  in  the  fuel,  less 
the  heat  required  in  the  evaporation  and  volatilization  of  con- 
stituents which  become  gaseous  at  the  temperature  resulting 
from  the  combustion  of  the  first-named  elements.  It  is  meas- 
ured in  "  thermal  units." 

A  thermal  unit  is  the  quantity  of  heat  necessary  to  raise  a 
unit  weight  of  water,  at  temperature  of  maximum  density,  one 
degree  of  temperature.  The  British  thermal  .unit  is  the  quan- 
tity of  heat  required  to  raise  a  pound  of  water  from  the  tem- 
perature 39°. i  to  40°.  i  Fahr.  The  metric  unit  or  calorie  is  the 
quantity  of  heat  required  to  raise  one  kilogramme  of  water 
(2.2046215  pounds)  from  3°. 94  to  4°.94  Centigrade. 

One  metric  or  centigrade  unit  is  equal  to  3.96832  British 
units,  and  a  British  unit  is  equal  to  0.251996  metric  unit. 

An  approximate  estimate  of  the  number  of  thermal  units 
developed  by  the  combustion  of  a  pound  or  kilogramme  of  any 
dry  fuel,  of  which  the  chemical  composition  is  known,  may  be 
obtained  by  the  use  of  the  following  formula : 


h  =  i4,5oo(7  +  62,000(11  —  --], 


.     .    .    (i) 


THE   STEAM-BOILER. 

where  h  is  the  number  of  British  thermal  units  representing  the 
total  heat  of  combustion  of  one  pound  of  the  fuel ;  h'  is  the 
number  of  metric  units  per  kilogramme  of  fuel ;  C  represents 
the  percentage  of  carbon,  H  that  of  hydrogen,  and  O  that  of 
oxygen. 

Thus  an  anthracite  coal  has  been  found  to  have  the  follow- 
ing composition : 

COMPOSITION  OF  ANTHRACITE  COAL. 

Per  cent. 

Carbon 8 1 . 34 

Hydrogen,  uncombined 3-45 

Hydrogen,  in  combination o. 74 

Oxygen  and  Nitrogen 5 . 89 

Sulphur 0.64 

Water «. 2 .  oo 

Ash 5 .94 


Total 100.00 

One  pound  or  kilogramme  of  coal,  of  which  the  above  is  an 
analysis,  can  evaporate  theoretically  14.4  pounds  or  kilogrammes 
of  water  from  and  at  100°  Centigrade,  or  212°  Fahr. 

M.  M.  Scheurer,  Kestner,  and  Meunier  have  adopted  the 
common  formula  as  first  proposed  by  Dulong,  but  would  omit 
all  account  of  oxygen,  thus  reducing,  as  is  claimed,  the  average 
error  of  the  formula  from  about  12  per  cent  or  more  to  8 
or  10.  M.  Cornut  would  separate  the  fixed  from  the  volatile 
carbon,  and  would  give  the  latter  about  one  third  more  credit 
for  heating  power  than  the  former ;  closer  approximations  are 
thus  made  than  by  the  other  methods. 

Various  methods  of  approximate  determination  of  the 
heating  power  of  fuels  have  been  proposed.  The  use  of  the 
calorimeter  is  probably  the  most  satisfactory ;  another  method 
is  that  of  computation  from  the  known  chemical  composition 
of  the  fuel,  and  the  law  of  Walter,  who  found  the  quantity  of 
heat  produced  in  combustion  very  closely  proportional  to  the 
weight  of  oxygen  absorbed.  Berthier's  method  is  often  em- 
ployed :  this  consists  in  heating  the  fuel  sample  to  a  red  heat, 
in  a  closed  vessel,  with  litharge  or  other  source  of  oxygen. 
When  lead  oxide  is  thus  used,  the  weight  of  lead  reduced  to 


THE  FUELS  AND    THEIR   COMBUSTION.  I/I 

the  metallic  state  is  a  measure  of  the  oxygen  absorbed.  The 
method  is  simple  and  easy  of  practice,  but  is  not  sufficiently 
accurate  to  be  generally  approved. 

The  value  of  h  or  of  h'  ranges  between  5500  British  or  1386 
metric  units  for  dry  wood,  and  16,000  or  4032  for  the  best 
known  coals.  The  equation  given  is  deduced  from  the  experi- 
ments of  MM.  Fayre  and  Silbermann,  who  determined  the 
total  heat  of  combustion  of  one  pound  of  pure  carbon  to  be 
14,500  British  or  3654  metric  thermal  units,  and  of  one  pound  of 
hydrogen  to  be  62,000  British  units,  or  15,624  calories.  The 
combustion  of  one  kilogramme  of  each  would  develop  31,967 
British  or  8080  metric  units,  and  136,686  British  or  34,462 
metric  units,  respectively. 

The  combustion  of  the  several  kinds  of  carbon  produces  the 
development  per  unit  of  weight  of : 

British  Units.  Metric  Units.  Material. 

13,986.  . .    7,770 .Diamond. 

13,968 7,760 Iron  Graphite. 

14,040 7,800 Natural  Graphite. 

14,490 8,050 Gas  Carbon. 

14,500 8,080 Wood  Charcoal. 

Where  the  chemical  composition  of  the  fuel  is  unknown 
and  cannot  be  readily  ascertained,  its  heating  effect  may  be 
determined  experimentally  by  burning  a  known  weight  and 
passing  the  products  of  combustion  through  a  calorimeter  of 
such  area  of  heating-surface  as  to  reduce  their  temperature  very 
nearly  to  that  of  the  atmosphere  before  discharging  them. 

The  table  given  hereafter  exhibits  the  total  heating  effect 
of  various  fuels  as  estimated  from  analyses  of  good  specimens. 

Where  the  heat  produced  is  not  so  thoroughly  utilized  as  to 
cause  the  condensation  of  vapors  which  may  pass  off  with  the 
permanent  gases  resulting  from  combustion,  there  is  necessarily 
a  greater  loss  of  the  heat  of  combustion  of  hydrogen  than  of 
that  of  carbon,  and  the  relative  heating  efficiency  of  carbon  is 
considerably  increased  by  the  facts  that  it  must  be  raised  to 
red  heat  as  a  solid  before  combustion  can  occur,  and  that  the 
specific  heat  of  carbonic  acid  (0.216)  is  only  about  one  half  that 
of  aqueous  vapor  (0.475). 


I72  THE   STEAM-BOILER. 

The  general  formulas,  as  given  by  Watts,  for  ascertaining 
the  thermal  effect  of  any  fuel  of  a  known  composition  are  as 
follows : 

For  combustion  in  oxygen  : 


~ 


s.3.67C+9H+s'W 
For  combustion  in  air : 

T=- 


Here     T=  increase  of  temperature  produced  by  combus- 
tion ; 
£7  and  H  ==  quantities  of  carbon  and  hydrogen  available  in 

I  part  by  weight  of  the  fuel ; 
W=  total   quantity  of  water  yielded  by  I  part  by 

weight  of  the  fuel ; 
/  =  latent  heat  of  water  ; 
s,  sf,  s",  s'"  —  specific    heat    of    carbonic    acid,   water-vapor, 

nitrogen,  and  air ; 
c  and  c'  =  calorific  power  of  carbon  and  hydrogen ; 

N '=  quantity  of  nitrogen  in  air  necessary  for  con- 
verting combustible  constituents  of  I  part  by 
weight  of  fuel  into  carbonic  acid  and  water ; 
A  =  extra  quantity  of  air  supplied  for  combustion. 

76.  The  Temperature  of  the  Fire  depends,  not  solely  on 
the  amount  of  heat  generated  by  combustion,  but  also  on  the 
quantity  and  nature  of  the  resulting  products  of  combustion. 

The  total  heat  generated  by  the  combustion  of  fuel  is  all 
communicated  to  the  products  of  combustion,  which  are  usu- 
ally gaseous,  giving  them  a  temperature  which  is  determined, 
partly  by  the  calorific  power  of  the  fuel,  and  partly  by  their 
nature.  Thus,  carbon  requires  for  its  combustion  to  carbonic 


THE  FUELS  AND    THEIR    COMBUSTION.  173 

acid  2.67  times  its  weight  of  oxygen,  producing  3.67  times  its 
weight  of  carbonic  acid. 

The  heat  generated  by  combustion  of  carbon  is  capable  of 
raising  8080  times  its  weight  of  water  from  4°  to  5°  C.,  and 
would  raise  the  temperature  of  water  equal  in  weight  to  the 
carbonic  acid  produced,  about  2202°  C.*  —  i.e.,  8080  X  i°  = 
2201°.  63  X  3.67. 

But  the  specific  heat,  or  capacity  for  heat,  of  water  is 
greater  than  that  of  carbonic  acid  ;  the  increase  of  temperature 
in  the  carbonic  acid  produced  is  correspondingly  greater  than 
the  rise  in  temperature  that  would  be  produced  in  a  quantity 
of  water  equal  to  3.67  times  the  weight  of  carbon  burnt.  The 
quantities  of  heat  necessary  to  produce  equal  increase  of  tem- 
perature in  equal  weights  of  carbonic  acid  and  of  water  being 
in  the  proportion  of  0.2164  :  i.oooo,  the  amount  of  heat  needed 
to  raise  the  temperature  of  3.67  parts  water  and  3.67  parts  car- 
bonic acid  one  degree,  are  as 


3-67 


3.67  X  0.2164       0.794* 

Hence  the  rise  in  temperature  of  the  3.67  parts  of  carbonic 
acid,  to  which  the  heat  of  combustion  of  i  part  carbon  is  trans- 
ferred, maybe  calculated  by  dividing  the  given  number  of  heat- 
units  by  the  amount  of  heat  required  to  raise  the  temperature 
of  the  3.67"  parts  carbonic  acid  one  degree,  or 


.  =  ,8,345°  F. 


The  heat  of  combustion  of  hydrogen  is  sufficient  to  raise 
the  temperature  of  34,462  times  its  weight  of  water  4°  to  5° 
Cent.,  but  it  requires  for  its  combustion  8  times  its  weight  of 
oxygen,  and  produces  9  times  its  weight  of  vapor.  The  prod- 

*  Watts'  Dictionary  of  Chemistry. 


174  THE   STEAM-BOILER. 

ucts  of  combustion  weigh  nearly  2-J-  times  as  much  as  those  of 
the  combustion  of  an  equal  weight  of  carbon.  Some  of  the 
heat  produced  by  the  combustion  of  hydrogen  becomes  latent 
and  does  not  increase  the  temperature  of  the  gases. 

The  latent  heat  of  water,  or  that  needed  to  convert  I  part 
of  water  at  100°  C.  into  steam,  is  537  times  as  much  as  is 
needed  to  raise  the  temperature  of  an  equal  weight  of  water 
from  4°  to  5°  C.,  and  966.1  times  the  quantity  which  will  raise 
the  temperature  of  one  part  from  39°.  I  to  40°. I  Fahrenheit. 
The  quantity  of  heat  latent  in  the  9  parts  vapor  produced  by 
the  combustion  of  hydrogen  will  therefore  be  4833  metric  heat- 
units  ;  this  must  be  taken  from  the  total  amount  of  heat  gen- 
erated in  calculating  the  quantity  of  heat  producing  rise  in 
temperature. 

Parts  by      Metric  British 

weight  of      Heat-  Heat- 

water  vapor,    units.  units. 

Total  heat  of  combustion  of  I  part 

hydrogen 34, 462  62,000.0 

Latent  heat  of  water  in  heat-units. .     gX  537=    4,833     9X966.1=    8,694.9 

Available  heat , 29,629  =  53,305.1 

The  specific  heat  of  water  vapor  is  0.475  J  the  heat  raising 
the  temperature  of  9  parts  water  and  9  parts  water  vapor  have 
the  proportion 

9Xi  9 


9  X  0.475       4-275' 
and  the  rise  in  temperature  will  be 

29629  _          0  0 

4«275 

Thus  the  heating  and  the  calorific  power  are  not  necessarily 
the  same.  The  heating  effect  depends  only  partly  upon  the 
calorific  power  of  the  fuel  burnt. 


THE  FUELS  AND    THEIR   COMBUSTION. 


175 


RECAPITULATION.     (WATTS.) 


Weight. 

Weight  of 
Oxygen. 

Ratio. 

Weight  of 
Products. 

Ratio. 

Heat- 
units. 

Ratio. 

Thermal 
Effect. 

Ratio 

Carbon.  .  .  . 

I 

2.67 

I 

3.67 

I 

8080 

I  .OOO 

10176° 

1.  000 

Hydrogen.. 

I 

8 

3 

9.OO 

2.4 

34,462 

4.265 

6930.7° 

0.681 

In  these  examples  combustion  takes  place  in  oxygen,  and 
with  no  more  than  is  theoretically  needed.  In  all  actual  cases 
of  combustion,  atmospheric  air  supplies  the  oxygen  supporting 
the  combustion.  Nitrogen,  of  which  it  contains  77  per  cent, 
dilutes  the  products  of  combustion  and  reduces  the  tempera- 
ture. In  the  case  of  combustion  of  carbon  in  air,  the  nitro- 
gen in  air  containing  2.67  parts  of  oxygen  amounts  to  8.94  by 
weight. 

The  specific  heat  of  nitrogen  is  0.244,  and  the  quantity  of 
heat  needed  to  raise  the  temperature  of  the  nitrogen  from  4° 
to  5°  C.  is: 

8.94  X  0.244  =  2.181  units. 

Adding  to  this  the  heat  needed  to  raise  the  temperature  of 
the  carbonic  acid  produced,  the  amount  of  heat  needed  to  raise 
the  temperature  of  all  the  products  of  combustion  in  air  from 
4°  to  5°  C.  will  be 

2.181  +0.794  =  2.975  units. 
And  the  elevation  of  temperature  will  be 


~  =  2715°  C.  =  4887°  F. 


Burning  hydrogen  in  air,  the  nitrogen  in  air  containing  8 
parts  of  oxygen  is,  by  weight,  26.78  parts,  and  the  amount  of 
heat  needed  to  raise  its  temperature  from  4°  to  5°  C.  is: 

26.78  X  0.244  —  6.534  units, 


THE   STEAM-BOILER. 

and  the  consequent  rise  in  temperature  will  be 


S— i =  274J 

4.275  +  6.534         '* 


C.  -  4934°  F. 


The  difference  between  the  temperatures  attainable  by  the 
combustion  of  carbon  and  hydrogen  in  oxygen  and  in  air  is 
much  the  greatest  with  carbon,  as  the  quantity  of  heat  pro- 
duced by  its  combustion  is  much  less  than  that  generated  by 
burning  hydrogen,  thus : 


RECAPITULATION.    (WATTS.) 


Calorific 
Power. 

Ratio. 

TEMPERATURE  PRODUCED. 

Dif- 
ference. 

Ratio. 

In 
Oxygen. 

Ratio. 

In  Air. 

Ratio. 

Carbon 

8.080 
34-400 

1.  000 

4-265 

10,174° 
6,930° 

1.  000 

0.68] 

2,715° 
2,741° 

1.002 
I.OOQ 

7,459 
4,189 

1.  000 

0.561 

Hydrogen     . 

Thus  in  all  cases  where  high  temperatures  are  demanded,  it 
is  of  advantage  to  increase  the  amount  of  oxygen  in  the  air 
supporting  combustion,  and  to  restrict  the  influx  of  nitrogen 
and  of  superfluous  air.  Thus  also  the  reason  of  the  attainment 
of  high  temperatures  by  combustion  in  pure  oxygen  with  the 
oxyhydrogen  blow-pipe  is  readily  seen. 

The  quantity  of  air  supplied  is  usually  much  greater  than 
that  simply  required  to  furnish  the  oxygen  to  consume  the 
combustible.  In  practice  it  often  amounts  to  twice  as  much, 
and  is  rarely  less  than  one  and  a  quarter  times  the  quantity 
theoretically  needed,  and  there  consequently  follows  a  propor- 
tionate reduction  of  the  temperature  attainable.  When  carbon 
is  burnt  with  twice  as  much  air  as  is  theoretically  needed,  the 
products  of  combustion  have  24.22  times  the  weight  of  the  car- 
bon, and  with  hydrogen  80.56  times  the  weight  of  the  hydro- 
gen. 


THE  FUELS  AND    THEIR   COMBUSTION. 


AIR  REQUIRED  TO  SUPPLY  A   DOUBLE  AMOUNT  OF  OXYGEN. 


Parts  by  Weight 
ot  Air. 

Volume  of  Air  at 
60°  F.  per  Lb.  of 
Fuel,  Cubic  Feet. 

Parts  by  Weight  of 
Gaseous  Products. 

Carbon  I  .  . 

23.22 

303  .  39 

-25.22 

Hydrogen                      I 

70   ^6 

908  .  62 

80.56 

The  specific  heat  of  air  is  0.2377,  and  the  quantities  of  heat 
needed  to  raise  the  temperature  of  the  air  demanded  from  4° 
to  5°,  and  the  temperature  resulting  from  combustion  are : 

Combustion  of  carbon : 

2.7597=  ii.6rx  0.2377, 
8080 


and 


-.=  1408°  C. 


and 


2.759  +  2.975 
Combustion  of  hydrogen : 

34.78  X  0.2377  =  8.2672, 
29,629 


8.2672  +  io.8o93 


It  is  evidently  always  desirable  to  secure  perfect  combustion, 
and  with  the  least  possible  air-supply.  With  the  forced  draught 
produced  by  a  fan  or  blast-pipe,  fuel  may  be  burnt  with  less  air 
than  with  a  chimney  draught,  and  can  be  utilized  with  greater 
economy  of  heat.  This  economy  is  greater  with  fuel  contain- 
ing but  little  volatilizable  matter. 

Dissociation  is  a  phenomenon  which  probably  rarely  if  ever 
occurs  in  familiar  practice.  Oxygen  and  hydrogen,  combined 
to  form  water,  or  steam,  at  ordinary  furnace  temperatures,  are 
separated  again  by  heat-energy  when  the  temperature  is  some- 
where below  6000°  Cent.  (10,832°  Fahr.).  St.  Claire  Deville,  the 
first  to  observe  and  study  this  phenomenon,  concluded  that  dis- 


12 


1  78  THE   STEAM-BOILER. 

sociation  may  commence  at  1000°  Cent.  (1832°  Fahr.)  or  below 
that  heat.*  Deville  and  Debray  reported  the  temperature  of 
the  common  oxyhydrogen  flame  to  be  not  above  2500°  Cent. 
(4532°  Fahr.),  and  Bunsen  found  that  under  increasing  pres- 
sures the  temperature  limit  as  fixed  by  dissociation  was  raised 
until,  at  ten  atmospheres,  it  had  increased  ten  per  cent  or  more. 
77.  The  Minimum  Quantity  of  Air  required  for  the  per- 
fect combustion  of  any  kind  of  fuel  may  be  readily  calculated 
from  its  known  chemical  constitution. 

.   Calling  the  weight  of  air  W,  and  denoting  the  weights  of 
carbon,  hydrogen,  and  oxygen,  C,  H,  and  O, 


(4) 


The  value  of  Granges  from  6  for  dry  wood,  to  12  for  an- 
thracite and  good  bituminous  coal.  Charcoal  and  the  softer 
bituminous  coals  require  about  1  1  parts  by  weight  of  air  per  I 
part  of  fuel. 

These  values  can  only  be  approximated,  in  practice,  with 
extremely  slow  and  carefully  managed  combustion.  A  perfect 
intermixture  of  the  combustible  with  the  supporter  of  combus- 
tion can  only  be  secured  by  the  admission  of  some  excess  of  air 
to  the  furnace.  Probably  about  double  the  estimated  amount 
of  air  is  usually  provided,  although  in  some  cases,  where  a 
forced  draught  produces  exceptionally  complete  intermixture 
of  the  gases,  the  quantity  may  be  brought  as  low  as  18  pounds 
of  air  per  pound  of  coal. 

In  one  instance,  in  which  a  furnace  burning  wet  fuel  was 
tested  by  the  Author,  to  determine  its  economic  efficiency,  the 
quantity  of  air  supplied  was  very  little  in  excess  of  that  dictated 
by  theory.  This  was,  however,  an  exceptional  case.  As  the 
excess  of  air  must  be  heated  to  the  temperature  of  the  chimney, 
and  then  thrown  away,  it  causes  a  notable  waste  of  heat. 

The  weight  of  a  cubic  foot  of  air  at  mean  atmospheric  tem- 
perature being  0.076361  pound,  the  volume  of  air  required  for 


Archives  des  Sciences  Physiques,  1860,  t.  ix.,  p.  51. 


THE  FUELS  AND    THEIR   COMBUSTION.  1 79 

perfect  combustion,  in  any  case,  may  be  determined  by  the 
equation : 


(5) 


Eighteen  and  twenty-four  pounds  of  air,  required,  as  stated 
above  for  combustion,  in  the  case  mentioned,  of  one  pound  of 
coal,  would  measure,  respectively,  236  and  314  cubic  feet. 

The  weight  of  a  cubic  metre  of  air  is  1.224  kilogrammes. 
The  volume,  in  metric  measures,  required  in  any  case  is  there- 
fore 


(6) 


When  eighteen  and  twenty-four  times  the  weight  of  fuel 
are  required  respectively,  the  volumes  in  the  case  taken  would 
be  15  and  19  cubic  metres. 

78.  The  Temperature  of  the  Products  of  Combustion 
may  be  calculated,  as  has  been  shown,  with  approximation  to 
accuracy,  from  the  known  weight  of  the  fuel  and  of  the  prod- 
ucts of  combustion,  the  heat-generating  power  of  the  former, 
and  the  specific  heat  of  the  latter. 

The  specific  heat  of  the  products  of  combustion  are,  at  con- 
stant pressure,  and  for  equal  weights : 

SPECIFIC  HEATS  OF  PRODUCTS  OF  COMBUSTION.    (REGNAULT.) 

(Water  =  I.     Pressure  constant.') 

Air 0.2374 

Oxygen 0.2175 

Nitrogen .  0.2438 

Steam o. 4805 

Carbonic  acid 0.2164 

The  proportions  in  which  these  substances  occur  in  the  prod- 
ucts of  combustion  being  known,  the  mean  specific  heat  of  all 
may  be  determined  ;  and  the  total  heat  of  combustion  of  one 
pound  of  fuel  being  divided  by  the  product  of  this  weight  by 


180  THE    STEAM-BOILER. 

this  mean  specific  heat,  the  quotient  is  the  probable  tempera- 
ture of  the  furnace  gases. 

Rankine  gives  the  result  of  this  calculation,  in  cases  where 
carbon  alone  is  burned  with  undiluted  air,  and  diluted  with  one 
half  and  with  equal  weight  of  additional  air,  respectively,  4580°, 
3215°,  and  2440°  Fahr.,  equal  to  2627°,  1824°,  and  1338°  Cent. 

Olefiant  gas,  similarly  treated,  should  give  temperatures  of 
5050°,  35 15°,  and  2710°  Fahr.;  or  2788°,  1953°,  and  1488°  Cent 

The  mean  specific  heat  of  the  products  of  combustion  is 
practically  equal  to  the  specific  heat  of  air. 

The  following  are  the  specific  heats  given  by  Rankine : 

SPECIFIC   HEAT   UNDER  CONSTANT  PRESSURE. 

Carbonic-acid  gas 0.217 

Steam 0.475 

Nitrogen,  probably 0-245 

Air 0.238 

Ashes o .  200 

Durham  (British)  coke,  having  the  composition  (Deering) 
of— 

Carbon  93-78 

Sulphur 0.82 

Ash 5.40 


Total 100.00 

liberates  13,640  British  thermal  units  per  pound  and  requires 
10.91  pounds  of  air  per  pound  of  fuel,  for  complete  combustion, 
the  heat  produced  being  1 145  units  per  pound,  the  resultant 
rise  in  temperature  being  4877°  F.  (2709°  C),  and  the  amount 
of  water  evaporated,  as  a  maximum,  being  14.12  times  the 
weight  of  the  coke. 

The  best  bituminous  coalcontains,  as  an  example, 

Carbon 81 . 47 

Hydrogen 4-97 

Nitrogen i .  63 

Oxygen 5.32 

Sulphur 1 . 10 

Ash 5.51 

Total ...........  100  oo 


THE  FUELS  AND    THEIR   COMBUSTION.  l8l 

Its  complete  combustion  requires  10.99  times  its  weight  of 
air,  giving  a  rise  of  temperature  of  4830°  F.  (2683°  C.)  and  an 
evaporation  of  14.64  times  its  weight  of  water  from  and  at  the 
boiling-point.  The  heat  produced  is  14,143  units  per  pound 
of  fuel,  or  1 1 8°  per  pound  of  furnace  gases. 

Oak  wood,  according   to   Deering,*  has  the  composition, 
when  kiln-dried, 

Oxygen. . . . . 41.27 

Hydrogen. 6.00 

Nitrogen ...... 1.13 

Carbon. 49-95 

Ash 1.65 


Total 100.00 

It  will  evaporate  7.98  times  its  own  weight  of  water,  develop- 
ing 7713  British  heat-units  per  pound,  demanding  6.08  times 
its  own  weight  of  air  for  complete  combustion,  the  products  of 
combustion  containing  1089  heat-units  per  pound  and  attaining 
a  temperature  of  4287°  F.  (2382°  C). 

Pennsylvania  petroleum,  having  the  composition,  according 
to  Deering,  of 

Carbon   ........ 85  j  Hydrogen. . 15 

requires  15  times  its  own  weight  of  air  for  complete  combus- 
tion, liberates  20,360  British  thermal  units  per  pound  of  the 
liquid,  or  1267  per  pound  of  products  of  combustion,  and  de- 
velops an  increase  of  temperature  of  4900°  F.  (2722°  C.). 

Illuminating   gas,   according   to    Mr.  Deering,  having  the 
composition, 

Carbon 61.26 

Hydrogen 25.55 

Nitrogen 8.72 

Oxygen 4-47 


Total 100.00 

develops  20,801  British  thermal  units  per  pound,  equivalent  to 

*  Howard  Lecture.     W.  Anderson.     London,  1885. 


1 82  THE   STEAM-BOILER. 

the  evaporation  of  21.53  times  its  own  weight  of  water,  the 
best  mixture  for  complete  combustion  being  15.66  parts  of  air, 
by  weight,  to  one  of  the  gas.  The  rise  in  temperature  with 
perfect  combustion  is  4567°  F.  (2537°  C),  the  total  heat  liber- 
ated being  1250  British  thermal  units  per  pound  of  the  mix- 
ture. 

The  same  gas,  per  1000  cubic  feet,  weighs  as  follows : 

Carbon 18.19  Ibs. 

Hydrogen./ 7-58    " 

Nitrogen.... 2.59    " 

Oxygen 1.33    " 


Total 29 . 69  Ibs. 

It  produces  617,485  units  of  heat,  and  can  evaporate  639  pounds 
of  water,  demanding  465  pounds  of  air  for  complete  combus- 
tion. 

By  using  the  data  of  Rankine,  results  are  obtained  for  the 
two  extreme  cases  of  pure  carbon  and  olefiant  gas,  burned  re- 
spectively in  air  ;  British  units  are  used  thus : 

Carbon.  Olefiant  Gas. 

Total  heat  of  combustion  per  pound 14,500  21,300 

Weight  ot  products  of  combustion  in  air,  undiluted 13  Ibs.  16.43  Ibs. 

Their  mean  specific  heat 0.237  0.257 

Specific  heat  X  weight 3.08  4.22 

Elevation  of  temperature,  if  undiluted 4,580°  5,050° 

If  diluted  with  air  =  -J-  air  for  combustion. 

Weight  per  lb.  of  fuel. .. 19.  24.2 

Mean  specific  heat 0.237        0.25 

Specific  heat  X  weight 4.51  6.06 

Elevation  of  temperature 3,2I5°       3,5I5° 

If  diluted  with  air  =  air  for  combustion. 

Weight  per  lb.  fuel 25.  31.86 

Mean  specific  heat. o. 238  o. 248 

Specific  heat  X  weight 5-94  7-9 

Elevation  of  temperature 2,440°  2,710° 

For  wet  fuel,  like  sawdust,  or  spent  tan  from  the  leach,  the 
Author  has  made  the  following  estimation  in  one  actual  case 


THE  FUELS  AND    THEIR   COMBUSTION.  183 

where  the  fuel  consists  of  45  per  cent  of  woody  fibre,  and  55 
per  cent  of  water. 

Taking  the  available  heat  per  pound  of  the  dry  portion  at 
6480  British  thermal  units,  each  pound  of  wet  fuel  yields  2916 
units  of  heat.  Of  this,  531.6  are  absorbed  in  the  evaporation 
of  the  55  per  cent  of  water,  leaving  2384.4  units  to  raise  the 
temperature  of  the  products  of  combustion.  Of  these  there 
are,  as  a  minimum,  3.7  pounds,  having  a  mean  specific  heat  of 
about  0.287. 

The  elevation  of  temperature  is  therefore  2245.3°  Fahr., 
and  adding  the  mean  temperature  of  the  atmosphere,  74°,  the 
mean  temperature  of  furnace,  assuming  no  dilution  with  un- 
used air,  and  no  losses,  would  have  been  about  2320°  Fahr. 
(1271°  Cent.).  Losing  2\  per  cent  by  radiation  and  conduc- 
tion, etc.,  the  actual  temperature  was  2260°  Fahr.  (1238°  Cent.). 

The  temperature  of  chimney  flue  was  found  by  experiment 
to  have  been  544°.  The  furnace  gases  were  therefore  cooled 
2260°  —  544°  =  1716°  Fahr.  (937°  Cent.)  by  the  loss  of  the 
heat  given  up  to  the  boiler.  This  is  equivalent  to  1716X0.287 
=  492.5  British  heat-units  per  pound  of  gas,  and  to  4049.4 
units  per  pound  of  ligneous  material  in  the  fuel. 

The  "  equivalent  evaporation,"  from  and  at  212°,  is  4049.4 
-=-  966.6  =  4.18  pounds  of  water.  The  actual  evaporation  was 
equivalent  to  4.24  pounds,  and  the  difference — less  than  one  per 
cent  of  the  total — represents  losses  and  errors  of  calculation. 

The  actual  existing  temperature  of  furnace  can  be  also  thus 
estimated.  The  available  heat  per  pound  of  fuel,  including 
water,  has  been  given  at  2916  British  thermal  units.  Of  this 

531.6 

— — —  =  0.182  passed  off  with  vapor,  and  was  not  useful  in  rais- 
ing the  temperature  of  either  the  furnace  or  the  chimney. 
Hence,  of  all  heat  liberated,  i.oo  —  0.182  =  0.8 1 8  was  efficient 
in  elevating  the  temperature  of  furnace,  and  0.37  —  0.182 
=  o.i 88  was  effective  in  producing  the  observed  temperature, 
544°  Fahr.,  of  chimney.  Then,  since  the  same  quantity  of 
gas  passes  at  both  places,  the  temperature  of  furnace  was 

oT8S"  X  47°/  ~^~  74°  —  2II9°  Fahn     To  this  is  to  be 


1 84  THE   STEAM-BOILER. 

the  slight  loss  of  temperature  en  route  between  furnace  and 
chimney  by  conduction  and  radiation,  which  may  make  the 
figure  very  nearly  2260°  Fahr.,  as  above. 

The  actual  temperature  of  the  furnace  may  be  judged,  in 
any  case,  by  observing  the  brilliancy  of  the  light  radiated  from 
any  solid  in  its  midst,  and  presumably  at  its  own  temperature, 
as  by  the  following  table  given  by  Pouillet : 

Appearance.  Temp.  Fahr. 

Red,  just  visible 977° 

"      dull 1290 

"      cherry,  dull 1470 

full   1650 

"  "        clear 1830 

Orange,  deep  ...    2010 

"        clear 2190 

White  heat 2370 

"     bright r. . .  2550 

"     dazzling 2730 

To  determine  temperature  by  fusion  of  metals,  we  have 
also  from  the  same  authority — 

Substance.  Temp.  Fahr. 

Tallow 92° 

Spermaceti 120 

Wax,  white 154 

Sulphur 239 

Tin 455 

Metal. 

Bismuth 518 

Lead 630 

Zinc 793 

Antimony 810 

Brass  1650 

Silver,  pure 1830 

Gold  coin 2156 

Iron,  cast,  medium 2010 

Steel 2550 

Wrought-iron 2910 

79.  The  Rate  of  Combustion  is  determined  principally 
by  the  quantity  of  air  supplied.  The  amount  of  coal  burned 
per  square  foot  of  grate  with  chimney  draught  varies  very 


THE  FUELS  AND    THEIR   COMBUSTION.  185 

nearly  with  the  square  root  of  the  height  of  the  chimney,  and 
has  been  found  by  the  Author,  ordinarily,  to  be  very  nearly,  as 
a  maximum, 


W=2V7T-i, 


or 


where  W  and  W  are  weights  of  fuel  burned  per  hour  per 
square  foot  of  grate,  and  on  the  square  metre,  in  pounds  and 
kilogrammes,  and  H  and  H'  are  the  heights  of  chimney  in  feet 
and  metres. 

A  chimney  64  feet  or  19^-  metres  high,  will,  for  example, 
under  favorable  conditions,  usually  support  combustion  of  15 
pounds  of  coal  per  square  foot  of  grate,  or  of  73  kilogrammes 
per  square  metre.  The  weight  of  combustible  which  may  be 
burned  in  any  unit  of  time  may  be  calculated  approximately 
by  dividing  the  weight  of  air  which  can  be  supplied  in  that 
time,  by  its  proportion  to  weight  of  fuel,  as  determined  in  the 
preceding  paragraphs.  In  exceptional  cases  there  is  sometimes 
a  large  excess  of  air,  and  sometimes  a  considerable  deficiency. 
In  such  instances,  direct  experiment  only  can  determine  the 
amount  of  fuel  burned. 

80.  The  Efficiency  of  the  Furnace,  considered  as  a  heat- 
utilizing  apparatus,  is  determined  by  the  temperature  of  fur- 
nace gases,  by  the  thoroughness  with  which  complete  combus- 
tion is  secured,  and  with  which  losses  of  fuel  and  of  heat  are 
prevented.  It  is  measured  by  the  ratio  of  the  amount  of  the 
total  available  heat  oT  the  fuel  to  that  of  the  heat  actually  util- 
ized. This  efficiency  is  rarely  so  high  as  80  per  cent,  and  fre- 
quently falls  to  50  per  cent. 

In  all  cases,  efficiency  is  to  be  studied,  in  applications  of 
heat,  in  two  parts:  (i)  the  efficiency  of  the  heat-generating  and 
absorbing  apparatus,  i.e.,  the  furnace  ;  (2)  the  efficiency  of  the 
heat-utilizing  apparatus  and  methods,  as  the  steam-boiler,  the 
heating-chamber  of  the  reverberatory  furnace,  or  such  other 
heat-absorbing  arrangement  as  may  be  adopted. 

(i)  The  efficiency  of  the  furnace  is  represented  by 


r,  -  r; 


186  THE   STEAM-BOILER. 

in  which  E  is  the  ratio  of  the  heat  rendered  available  to  heat 
developed  ;  7\,  T^  7"3,  are  the  temperatures  of  furnace,  of 
chimney,  and  of  external  air.  For  examples,  in  two  actual 
cases,  Tlt  Tv  T3,  were,  2118°  F.,  544°  F.,  and  74°  F.,  or  1176°, 
302°,  or  510°,  251°,  and  48°  C.  for  the  second  case.  The  values 
of  the  efficiencies  of  the  two  kinds  of  apparatus  were 


2118°  -  544°         .  919°  ~  452 


or  for  Centigrade  degrees, 

1176°  -  302°  510°  -  251° 

-_—  -0  =  0.77;  and  ^-  -—  0-  =  0.56; 


the  first  being  nearly  40  per  cent  higher  than  the  second.  A 
certain  change  of  fuel  would  have  given  the  first  a  maximum 
temperature  of  2644°  F.,  1451°  C.,  and  would  have  raised  its 
efficiency  to 

2644°  -  544°  _ 


2644°-    74° 
or 

1451°  -  279° 
-    23° 


(2)  The  efficiency  of  the  heat-absorbing  apparatus  is  de- 
pendent upon  the  character  and  proportion,  and  is  not  treated 
here.  The  highest  efficiency  in  heat-production  is  secured  by 
perfect  combustion  with  the  least  practicable  air-supply,  thus 
obtaining  the  highest  possible  resulting  temperature. 

A  large  part  of  the  heat  produced  by  combustion  of  fuel 
is  expended  in  procuring  chimney  draught.  This  is  not  avail- 
able for  producing  any  other  useful  effects. 

The  amount  of  heat  thus  expended  varies  with  the  nature 
of  the  products  of  combustion,  and  the  use  to  which  the  heat 


THE  FUELS  AND    THEIR   COMBUSTION.  l8/ 

is  to  be  applied.  In  all  cases  the  heat  thus  discharged  is 
wasted. 

The  temperature  of  the  products  of  combustion  cannot 
usually  be  reduced  much  below  about  600°  F.,  or  315°  C. 

8l.  Economy  in  Combustion  of  Fuels,  where  they  are 
used  simply  in  the  production  of  high  temperature,  is  so  im- 
portant a  matter,  except  in  those  favored  localities  where  the 
proximity  of  coal,  or  of  peat-beds,  or  of  forests,  renders  its 
waste  less  objectionable,  that  the  engineer  should  omit  no 
precaution  in  the  endeavor  to  secure  their  perfect  utiliza- 
tion. 

To  secure  the  greatest  economy,  it  is  necessary  to  adopt  a 
form  of  grate  which,  while  allowing  a  sufficient  supply  of  air 
to  pass  through  it  to  insure  complete  combustion,  has  such 
narrow  air-spaces  as  to  prevent  waste  of  small  fragments,  by 
falling  through  them. 

The  narrower  the  grate-bars  and  the  air-spaces,  the  more 
readily  can  losses  from  this  cause  and  from  obstruction  of 
draught  be  avoided.  With  a  hot  fire,  however,  the  difficul- 
ties arising  from  the  warping  of  the  bars  become  so  great, 
that  it  is  only  by  peculiar  devices  for  interlocking  and  bracing 
them  that  their  thickness  can  be  reduced  below  about  -J  of  an 
inch  at  the  top.  Many  such  devices  are  now  in  use.  In  fur- 
naces burning  wet  fuel,  with  an  ash-pit  fire,  fire-brick  grate-bars 
are  used. 

A  certain  amount  of  air  must  usually  be  allowed  to  enter 
the  furnace  above  the  grate,  to  consume  those  combustible 
gases  which  do  not  obtain  the  requisite  supply  of  oxygen  from 
below.  The  carbon,  probably,  in  such  cases  usually  obtains 
its  oxygen  from  below  the  grate,  while  the  gaseous  constituents 
of  the  fuel  are  consumed  by  the  oxygen  coming  in  above. 

Chas.  Wye  Williams,  who  made  most  extended  and  care- 
ful experiments  on  combustion  of  fuel,  recommended,  for 
ordinary  cases,  where  bituminous  coal  was  burned,  a  cross  area 
of  passage,  admitting  air  above  the  grate,  of  one  square  inch 
for  each  900  pounds  of  coal  burned  per  hour,  or  about  one 
square  centimetre  for  each  63  kilogrammes  of  fuel.  This  area 
should  be  made  larger,  proportionally,  as  the  thickness  of  the 


1 88  THE   STEAM-BOILER, 

bed  of  the  fuel  is  increased,  and  as  the  proportion  of  hydrocar- 
bons becomes  greater. 

Chilling  the  gases,  before  combustion  is  complete,  should 
be  carefully  prevented ;  and  comparatively  cold  surfaces,  as 
those  of  a  steam-boiler,  should  not  be  placed  too  near  the 
burning  fuel.  A  large  combustion-chamber  should,  where 
possible,  be  provided,  and  more  complete  combustion  may  be 
expected  in  furnaces  of  large  size,  lined  with  fire-brick,  and 
with  arches  of  the  same  material,  than  in  a  furnace  of  small  size 
where  the  fire  is  surrounded  by  chilling  surfaces,  as  in  a  "  fire- 
box steam-boiler." 

Finally,  the  greatest  possible  amount  of  heat  being  devel- 
oped in  combustion,  careful  provision  should  be  made  for  com- 
pletely utilizing  that  heat. 

In  a  steam-boiler  this  is  accomplished  by  having  large  heat- 
ing-surfaces, and  by  so  arranging  the  distribution  of  the 
adjacent  currents  of  water  and  of  hot  gases  that  their  differ- 
ence of  temperature  shall  be  the  greatest  possible.  The  gases 
should  enter  the  flues  at  that  part  of  the  boiler  where  the  tem- 
perature is  highest,  and  leave  them  at  the  point  of  lowest  tern 
perature.  The  feed-water  should  enter  as  near  as  possible  to 
the  point  where  the  gases  pass  off  to  the  chimney,  and  should 
gradually  circulate  until  evaporation  is  completed  at,  as  nearly 
as  possible,  that  part  of  the  boiler  nearest  to  the  point  of 
entrance  of  the  heated  gases. 

Where  a  small  combustion-chamber  is  unavoidably  employ- 
ed, as  in  locomotives,  various  expedients  have  been  devised 
with  the  object  of  producing  complete  intermixture  of  gases 
before  entering  the  tubes.  The  most  common  and  most  suc- 
cessful is  a  bridge-wall,  sometimes  depending  from  the  crown 
sheet,  but  sometimes  rising  from  the  grate,  and  which,  by  the 
production  of  eddies  in  the  passing  current,  causes  a  more 
thorough  commingling  of  the  combustible  gases  with  the 
accompanying  air.  None  of  these  devices  seem  yet  to  have 
given  such  good  results  as  to  induce  their  general  adoption. 

In  the  furnaces  of  steam-boilers  it  is  usually  considered 
advisable  to  allow  the  gaseous  products  of  combustion  to  enter 
the  chimney  at  a  temperature  of  about  600°  Fahr.  (315°  Cent.), 


THE  FUELS  AND    THEIR    COMBUSTION.  189 

or  about  2.08  times  the  absolute  temperature  of  the  external 
air,  where  natural  draught  is  employed.  Rankine  has  stated 
that  the  best  temperature  of  chimney  for  natural  draught  is 
that  at  which  the  gases  have  a  density  equal  to  about  one  half 
that  of  the  external  air.  Thus,  the  temperature  of  the  external 
air  being  60°  Fahr.  (15°. 5  Cent.),  its  absolute  temperature  is 
521°. 2  (261°. 75  Cent.),  and  the  required  absolute  temperature 
of  the  gases  in  the  chimney  will  be  this  temperature  multiplied 
by  2^3-,  i.e.,  521°. 2  X  2T^  =  1085°. 8,  and  the  corresponding 
temperature  on  the  ordinary  scale  is  624°. 6  Fahr.  (339°. 2  Cent.). 

With  forced  draught,  a  considerable  economy  may  be 
effected  by  the  reduction  of  the  temperature  of  escaping  gases 
approximately  to  that  of  the  boiler  itself  at  the  point  of  dis- 
charge of  the  gases. 

The  fuel  should  be  usually  burned  at  a  fair  rate  of  combus- 
tion, and  in  such  manner  as  to  give  that  degree  of  efficiency 
which  has  been  found  financially  desirable.  The  air-supply 
should  be  provided  for,  partly  above  as  well  as  below  the 
grates,  bituminous  coal  demanding  more  above  the  bed  of  fuel 
than  anthracite,  partly  because  it  is  needed  to  burn  the  gaseous 
hydrocarbons  driven  off  from  the  former,  and  partly  because 
the  bituminous  fuel  is  burned  in  a  thicker  and  less  permeable 
bed  of  fuel.  Ten  or  fifteen  per  cent  of  the  total  air-supply 
should  usually  be  furnished  above  the  flame-bed. 

The  grate-area  should  always  be  so  proportioned  that  it 
shall  be  possible  to  keep  it,  in  ordinary  working,  at  all  times 
well  and  uniformly  covered  with  incandescent  fuel.  The 
space  above  the  grate,  between  it  and  the  heating-surfaces, 
should  always  be  so  large  that  ample  space  and  time  are  given 
for  thorough  intermixture  of  gases  and  complete  combustion, 
and  it  should  have  such  form  that  the  air  introduced  above 
the  fuel  may  become  well  mingled  with  the  gases  distilled 
from  the  coal.  The  effect  of  this  air-supply,  where  bituminous 
coal  is  used,  is  well  shown  in  an  experiment  by  Mr.  Houlds- 
worth,*  made  in  1842  for  the  British  Association,  at  its  Man- 


*  Fuel  Combustion  and  Economy;  C.  W.  Williams.  "  On  the  Consumption  of 
Fuel,  etc.;"  Wm.  Fairbairn,  Trans.  Brit.  Assoc.  1842. 


190 


THE   STEAM-BOILER. 


Air  excluded  s                          i-     »--     H-     ^ 
State  of  the         o    o    o     o     S     o     c 
Flues. 

Air  admitted  J 
State  of  the 
Flues. 

0 

(  Clear  flame,    \ 
\  14  feet  long.  J 

0 

1—  ' 
Crt 

g     Ditto,  15  ft.  long. 
N: 

^     Ditto,  16  feet. 
&     Ditto,  15  feet. 
£     Ditto,  14  feet, 
g;     Ditto,  13  feet. 
§ 

Ct 

OS 

o 
^     Ditto,  13  feet. 

o 

^     Ditto,  15  feet. 
03       (  Purple  flame, 
0       |  from  carbonic 

co       (         oxide. 
on 

Very  black,      ) 

\ 

~~~*-~ 

"> 

^ 

Much  smoke     ) 

\ 

\ 

Ditto  

\ 

\\ 

\ 

} 

Ditt 

Dark  Eed     .    .    . 
Dingv  Eed   .     .     . 
Ditto,  no  flame      . 
Ditto  

\ 

\ 

• 

Dark  Eed    .     .    . 
Dark  

/•; 

/ 

P 

Ditto  

p 

Ditto  ..... 

0 

Ditto  

FUEL 

EVCLLf 

i 

Ditto  

\ 

ZL 

ELLED 

Dark  Eed     .    .    . 
Dark  

\ 

B 

Ditto  

/ 

/ 

' 

S 

Ditto  •'.«•«*.« 

J 

/ 

o 

*      -i'r         ^C-          *  S 

as     g   .  s       B" 

sl   8 1    S3     it          S" 

21!  21!    ? 

CO     O      O       fcO 
O     O      fcO       CO 

J13  5v-3 

•pspnioxa  .IIB    -panunpB  are 
•uoid  pio  no    '"Cl11  Aau  "O 

FIG.  69. — TEMPERATURE  OF  FURNACE. 


Chester  meeting.  As  seen  by  reference  to  Fig.  69,  the  tem- 
perature in  the  flue  fell  to  750°  F.  (400°  C.)  on  the  introduc- 
tion of  a  fresh  charge  of  fuel,  rose  at  the  end  of  a  half-hour 


THE  FUELS  AND    THEIR    COMBUSTION.  IQI 

to  above  1200°  F.  (650°  C),  then  fell,  until  at  the  end  of  an  hour 
and  a  quarter  it  had  dropped  to  1040°  F.  (560°  C.),  the  fire 
meantime  not  having  been  disturbed.  On  then  levelling  off 
the  surface  of  the  bed  of  fuel,  and  thus  filling  all  holes  in  the 
fire,  the  temperature  at  once  rose  nearly  to  the  maximum,  and 
then  gradually  fell  again  to  850°  F.  (454°  C.).  During  this 
period,  the  air  was  admitted  above  the  fire ;  the  lower  line  of 
the  diagram  shows  the  result  of  the  usual  method  of  handling 
the  fires  without  air-supply  above  the  fuel.  The  general 
method  of  variation  of  temperature  is  the  same  during  the 
period  between  successive  charges,  but  the  temperature  averages 
ten  per  cent  lower.  The  transformation  of  a  mass  of  black 
smoke  into  a  flame  many  feet  in  length  is  the  best  possible 
evidence  of  the  advantage  of  this  operation.  The  gain  in 
economy  of  fuel  was  estimated  at  about  one  third  when  the 
supply  of  air  was  properly  adjusted  and  managed.  The  dotted 
line  in  the  figure  indicates  the  probable  temperatures  when  the 
bed  of  fuel  is  kept  level  and  free  from  holes. 

82.  Weather  Waste. — When  coal  is  exposed  to  atmos- 
pheric influences,  a  "  weather  waste "  occurs.  Oxygen  is 
absorbed,  and  a  slow  combustion  injures  the  fuel.  Berthelot 
found  also  that  at  temperatures  not  exceeding  530°  Fahr. 
(277°  Cent.)  hydrogen  may  be  absorbed,  and  succeeded  in 
converting  two  thirds  of  the  bituminous  coal  experimented 
with  into  liquid  hydrocarbons.  Coals  freshly  mined  give  out 
gaseous  hydrocarbons,  and  even  anthracite  mines,  where  deep, 
are  not  free  from  danger  by  the  explosion  of  such  gases.  The 
absorption  of  oxygen,  and  this  loss  of  hydrogen  and  carbon,  is 
injurious  to  the  fuel.  According  to  Mursiller,  coals  containing 
41  fire-damp"  give  it  up  at  or  below  626°  Fahr.  (330°  Cent.), 
and  lose  their  coking  property.  Coals  usually  absorb  carbonic 
acid  freely. 

Poech  concludes  :*  "  Freshly-mined  coal  deposited  on  the 
rubbish  piles  is  capable  of  condensing  several  times  its  volume 
of  oxygen  in  its  pores.  The  oxygen  absorbed  enters  into 
chemical  combination  with  the  easily-oxidized  constituents. 

*  Van  Nostrand's  Magazine,  1884. 


1 92 


THE  STEAM-BOILER. 


According  as  the  absorption  is  rapid  or  slow,  a  greater  or  less 
elevation  of  temperature  is  produced.  In  the  former  it  may 
lead  to  spontaneous  combustion.  The  crumbling  of  coal  is, 
among  other  causes,  a  consequence  of  the  absorption  and  con- 
densation of  oxygen  in  its  pores,  and  the  chemical  changes  tak- 
ing place.  The  escape  of  the  hygroscopic  moisture  favors  the 
absorption  of  oxygen.  The  pyrites  can  only  produce  a  further- 
some  effect  on  the  increase  of  temperature  when  present  in 
considerable  quantities,  and  then  only  in  presence  of  moisture 
and  air ;  in  the  dry  state  they  must  be  regarded  as  perfectly 
passive,  and  may  even  be  detrimental  to  the  warming.  Freshly- 
mined  coal  placed  in  an  atmosphere  of  steam  can  suffer  no 
change.  Even  with  incomplete  exclusion  of  the  air  the  steam 
will,  in  general,  oppose  oxidation  and  warming,  principally  by 
uniform  moistening  of  the  pieces  of  coal." 

83.  The  Composition  of  the  Common  Fuels  may  be  ob- 
tained from  the  following  tables  : 


COMPOSITION  OF  VARIOUS   FUELS  OF  THE  UNITED   STATES. 


C. 

H.         0. 

N. 

S. 

Mois- 
ture. 

Ash. 

Spec. 
Grav. 

Pennsylvania  Anthracite       .  .    . 

78  6 

25       17 

0.8 

O  4 

I    2 

14   8 

I    .15. 

Rhode  Island           "         

85.8 

IO   5 

3-7 

85 

Q2.O 

6.0 

2.O 

.78 

North  Carolina        " 

83  i 

7  8 

Q    I 

Welsh                        "         

84.2 

a    7      2.^ 

O.Q 

O   Q 

1  .  3 

6   7 

4O 

Maryland  Semi-Bituminous  
Penna          "             " 

80.5 
75  8 

4-5   2.7^ 

2O    2 

I.  I 

1.2 

1-7 

8.3 

A     O 

•33 

•32 

/5-o 

CQ      A 

38  8 

i  8 

•2Q 

Indiana        "                            

70  o 

JU   .V 

28.0 

2   o 

24 

<  i               *  (             « 

c  2    o 

TQ  o 

9O 

27 

Illinois  Bituminous     .  . 

62  6 

-ic    5 

.«j 
I    Q 

OQ 

"        (Block)  Bituminous  
Ill  and  Ind  (Cannel)  Bituminous 

5&-2 

CQ      C 

37-1 

36  6 



.... 

.... 

4-7 
3    Q 

27 

Kentucky 

DV  0 

48.4 

48.8 

2.8 

•  25 

Tennessee  Bituminous     .  . 

71    O 

17   O 

12    O 

45 

41    5 

56   5 

2    C 

Alabama                          

K  I.O 

42   6 

I.O 

1.2 

1  .2 

55  -O 

41  .0 

4.O 

74   O 

18  6 

7   4 

Cal.  and  Oregon  Lignite  

5O.  I 

3.  0  13.  7 

0.9 

1  .5 

Tfi    7 

13.2 

1.32 

THE  FUELS  AND    THEIR   COMBUSTION. 


193 


MONONGAHELA  GAS  COAL.    (CRESSON.) 

Weight  of  sample,  60  Ibs.  (27.27  kilogrammes). 

Volatile  matter,  per  cent 35-74 

Coke,  per  cent 64 . 26 

Ash,  per  cent 6.66 

Yield  of  gas,  cubic  feet  per  pound  maximum 5.2 

44          44       cubic  metres  per  kilogramme  maximum. . . .  0.324 

Cubic  feet  per  pound  average 5.0 

"          "       cubic-metres  per  kilogramme  average 0.312:. 

Ton  maximum 11,648.0 

"     average 11,200.0 

Illuminating  power,  5  feet  per  hour  =  candles 15  .o< 

"               "         i  ton  coal  =  Ibs.  sperm 576.0 


COMPOSITION  OF  FOREIGN   COALS. 


C. 

H. 

N. 

O. 

S. 

Ash. 

Specific 
Gravity. 

Authority. 

Welsh  (Anthracite)  

00.4 

3-3 

0.8 

3.0 

O.g 

1.6 

1.32 

Vaux. 

Scotch           "            
English  (Newcastle)  

78.5 
82.1 

5-6 
5.3 

.0 
•4 

9-7 
5.7 

I.I 
I  .2 

4.0 

3-5 

1.26 
1.26 

Muspratt. 
.1 

••       (Lancashire) 

77    Q 

CO 

.  a 

Q.  C 

I  .4 

1  ft 

1  .27 

u 

14       (Derbyshire)      .  . 

7Q    7 

4.Q 

•4 

10.  3 

I  .O 

2.7 

I  .20 

il 

"       (Staffordshire) 

78.6 

K  .1 

8 

12.  Q 

0.4 

I.O 

Vaux. 

French  Anthracite   
"       Bituminous  

94.0 
84.0 

1.4 

5-0 

0.6 
i  .0 

"s'.o 

4.0 

2.0 

1-33 

Jacqueline. 
Ledieu. 

C.3.O 

4C 

.0 

7-O 

Johnson. 

German  (Silesia)       .         .     . 

C7   Q 

42 

.0 

2.  I 

1.26 

Saxony  

80.0 

IG 

.0 

I.O 

I.  20 

Prussia 

*6    7 

11 

Q 

24  4 

I    47 

Hindostan      ...                . 

CQ   O 

qe 

•  4 

14.6 

1  .  37 

Brazil     

C7.O 

4C 

.5 

r  6 

1  .2Q 

D/'V 

60.  7 

2t 

ft 

12.5 

1.33 

Cape  Breton 

67  6 

26 

•  Q 

c  .  e 

I    34 

Australia  (Lignite)  

64  3 

4.2 

I.O 

A  

IO.O 

o  6 

IO.O 

1.27 

Isherwood. 

Borneo      .        .          .       ... 

7O     3 

c  .4 

O.  7 

IQ    2 

I  .  2 

14   2 

I    37 

Muspratt 

Chili  ,  

70  6 

S.8 

I  .O 

13  .2 

2  .O 

7.4 

1  ,2Q 

Coke  

9r-5 

i-5 

7.0 

« 

13 


I94 


THE   STEAM-BOILER. 


COMPOSITION  OF  SUNDRY   FUELS. 


C. 

H. 

N. 

O. 

S. 

Ash. 

Specific 
Gravity. 

Authority. 

Wood  (kiln-dried)  
"      (air-dried)  
Peat  (kiln-dried)  

50-5 
40.4 
60.0 
46.1 

24.8 
52.2 

50.3 
71.8 
24.4 
14.0 
86.0 

86.5 
75-0 

85.7 

O.I 
4.9 

6.8 
4.6 

0.9 

1-3 
I.O 

40.7 
32.7 
30.0 
23.6 



1.6 

1.2 
I    Q 

0-5tO  1.2 

Watts. 
Paul. 

••     (air-dried)  

i-5 

2.8 

0.3 

O.  I 

1.5 
7-6 
13.6 

0-5 

Bitumen,  United  States.  .  .  . 
"          England     .    . 

Volatile 

Matter. 

.  

Johnson. 
Watts. 

7.0 
25.0 
14-3 

72.4 

47-5 
41.6 
26.7 
68.0 
72.6 
14.0 

France    

"          South  America.  .  . 

Petroleum,  pure  U.  S  

0.8 

"Dead  Oil"  

Refuse. 

1-5 

Gas    Marsh 

"     Olefiant      

Carb. 

Acid. 

Carb. 
Oxide. 

H. 

N. 

Hydro- 
carbon. 

Authority. 

Gas  from  Wood  

ii.  6 

•34.  c 

O.  7 

51.2 

Ebelmen. 

Charcoal  

0.8 

14.  I 

O.2 

64.0 

4       Peat  

14.0 

22-4 

O.5 

63.1 

« 

'      Coke 

i  "\ 

n.8 

O    I 

64  8 

ii 

'      Lignite  ...         . 

2    O 

40  o 

42.4 

3-2 

12.4 

'      Bituminous  Coal*.. 

4.1 

23.7 

8.0 

61.5 

2.2 

Siemens. 

*  Burned  in  Siemens'  gas-producers. 

84.  The  Heating  Effect,  or  calorific  power  of  good 
specimens  of  the  various  kinds  of  fuel,  is  given  in  the  follow- 
ing table,  expressed  in  British  thermal  units : 


THE  FUELS  AND    THEIR   COMBUSTION. 


195 


CALORIFIC    VALUE    OF    FUELS. 


FUEL. 

CALORIFIC 

:  POWER. 

Water 
vaporized 
at  Boiling- 

Cubic  Feet 
required 
to  stow 

Weight. 
Pounds 
per  Cubic 

Relative. 

Absolute. 

Parts  by 
one    Part. 

of  Furnace 
Coal. 

Foot  as 
stowed. 

Carbon  pure             

I  .OOO 

14  5OO 

15  .OO 

Hydrogen     

4.280 

62  500 

62.75 

1.816 

26,415 

26.68 

Olefia.nl  gas              

i  466 

21  ^28 

21  .  54 

Coal    Anthracite  

i  .020 

14  833 

14.08 

40  to  45 

40  to  56 

"      Bituminous 

I    OI7 

M7d6 

14.  QC 

42    to  4.8 

47  to  ^^ 

"      Lignite   dry      .          .  . 

O    7 

10  150 

IO.  ^5 

42 

57 

Peat   kiln-dried       

o.  7 

10  150 

10.25 

81 

25 

o.  526 

7  650 

7.73 

75 

3° 

\Vood   kiln-dried              

O    5^1 

8  O2Q 

$    IO 

"      air-dried    

o  4^0 

6  185 

6.45 

56  to  100 

22  tO  40 

Charcoal   

0.030 

i'?  =;oo 

14.00 

Coke  

0.040 

13,620 

14.00 

56  to  75 

30  to  40 

Petroleum,  heavy.  W.  Va.  .  .  . 
light,  W.  Va  
'                '*       Penna  

1.250 
1.260 
.240 

18,200 

18,350 

18,050 

18.75 
18.90 
18.60 

45 

50 

'           heavy    Ohio 

27O 

18  4.50 

IQ    O5 

'           Asia     .        

.240 

1  8  ooo 

18.60 

'            Europe  

.240 

1  8  ooo 

18.60 

Shale  Oil    France  (crude) 

24O 

1  8  ooo 

18.60 

Animal  fat     

o  650 

Q  OOO 

Q.  ^O 

The  difference  between  theoretical  and  effective  heating 
power  for  various  kinds  of  fuel  is  exhibited  in  the  following 
table,  which  gives  the  number  of  pounds  of  water  evaporated 
by  one  pound  of  fuel,  according  to  European  authorities : 


HEATING  POWER. 


FUEL. 

Theoretical. 

Under 
Steam  Boilers. 

Under 
Open  Boilers. 

Petroleum     

16  ^o 

10  o     to  14  o 

Anthracite   

12  45 

7.0     to  n.o 

Bituminous  Coal 

II    51 

52     to     80 

5   2 

Charcoal      

IO   77 

6.0     to     6.75 

a    7 

Coke  

9.0    to   10  8 

5.0     to     8  .0 

7-  7 

2.5     to     5.5 

1.5     to     2.3 

Peat               

55      to       i.A. 

25     to     50 

1.7      tO      2.3 

Wood  

4.3      to      5.6 

2.5     to     3.75 

1.85    tO      2.1 

Straw      . 

q   O 

I  86  to     I  92 

196 


THE   STEAM-BOILER. 


RELATIVE    VALUE    OF   VARIOUS    WOODS.    (OVERMAN.)* 


WOOD. 

Specific 
Gravity. 

Pounds 
in  one 
Cord. 

Per- 
centage 
Charcoal. 

Specific 
Gravity  of 
Charcoal. 

Pounds  of 
Charcoal 
in  a  Bush. 

Relative 
Value 
of  Wood. 

Hickory,  shell  bark..  .  . 
Oak   chestnut      

1.  000 

o  8Sq 

4.469 

3QC  C 

26.22 

22    7^ 

0.625 

o  481 

32.89 

2C      <J  T 

1.  00 
O   86 

0.885 

i  821 

21    62 

o  401 

21    IO 

O   8l 

Ash    white 

O   772 

3AC.Q 

2c    71 

28    78 

077 

Dogwood               .  .      . 

o.8m 

364.1 

2  1    OO 

O    ^  ^O 

O7C 

Oak   black       

0.728 

32C  i 

23  So 

o  187 

2O    36 

O    71 

•  '     red  

0.728 

•3    254 

22    41 

o  400 

2  1    O5 

o  60- 

Beech   white  

o  724 

1  2l6 

IQ   62 

o  m8 

27    26 

o  65 

Walnut    black 

o  681 

•5    O44 

22    ^6 

o  418 

22    OO 

O6e 

Maple,  hard  (sugar)...  . 
Cedar   red       

0.644 

o  e;6=; 

2,878 

2  C2=; 

21.43 

2_l    72 

0.431 

o  238 

22.68 
12    ^2 

O.6o 

o  56 

Magnolia   

o  60=; 

2  704 

21    CQ 

o  406 

21    36 

o  56 

Maple   soft 

O    ^Q7 

2  668 

2O   04 

O17O 

IO    J.7 

Oe/i 

Pine    yellow 

O    ^  I 

2  46l 

21    7-3 

O    II'S 

17    ^2 

OCA 

Sycamore      .        ... 

o  m^ 

2  1QI 

23    60 

O    274 

19  68 

O    ^2 

Butternut    

o.  c;67 

2   tC-71 

2O   7Q 

O   217 

1  2    J.7 

o  m 

Pine    New  Jersey  

0.478 

2   117 

24.88 

O    l8q 

2O    26 

O   4.8 

"      pitch 

o  426 

I  QO4 

26   76 

o  208 

15  68 

OA<\ 

"      white              . 

O   4l2 

i  868 

2.1    m 

O    2Q1 

I  ^    J.2 

O   4.2 

Poplar,  Lombardy.  .  .  . 

0.397 

O    5S2 

L774 

2  111 

25.OO 
2C    2Q 

0.245 
O    ^7Q 

12.85 
IQ    7J, 

O.4O 
O    ">2 

Poplar,  yellow...    

0.563 

2,5l6 

2I.8I 

0.383 

20.15 

0.52 

*  Metallurgy.     N.  Y. :  D.  Appleton  &  Co.,  1864. 

Wood  cut  in  January  contains  from  15  to  25  per  cent  less 
water  than  after  the  sap  is  in  motion  in  April.  As  wood 
seasons  naturally  in  the  air,  it  loses  from  one  sixth  to  one 
third  its  weight  of  water,  but  still  contains  from  one  seventh 
to  one  fourth  its  weight  of  moisture.  A  considerable  part  of 
the  latter  may  be  expelled  by  kiln-drying,  and  most  of  it  if  the 
kiln  heat  be  raised  to  212°.  A  cord  of  wood  contains  128 
cubic  feet  as  it  lies  piled  up.  But  allowing  for  the  interstices 
in  fairly  piled  wood,  we  may  reckon  a  cord  to  actually  contain 
about  seventy-two  cubic  feet.  Thoroughly  dry  wood  weighs 
nearly  as  follows : 

One  cubic  foot. 
62 

53 

49 

45* 

45 


Hickory,  pounds, 

White  oak 

White  ash 

Red  oak 

White  beech. . 


One  cord. 
4,464 
3,816 
3,528 
3,276 
2,240 


THE  FUELS  AND    THEIR   COMBUSTION.  197 

One  cubic  foot.        One  cord. 

Apple  tree 43  3,096 

Black  birch 43  3,096 

Black  walnut 42$  3,060 

Hard  maple 40  2,880 

Soft  maple 37  2,664 

Wild  cherry 37  2,664 

White  elm 36^  2,628 

Butternut 35i  2,556 

Red  cedar 35  2,520 

Yellow  pine » 34  2,447 

White  birch 33  2,376 

Chestnut 32  2. 304 

White  pine 26  1,872 


With  hickory  at  $5  a  cord,  other  woods  are  worth  about  as 
below  : 

Hickory $5  oo 

White  oak 4  05 

White  ash , 3  85 

Apple ,  3  50 

Red  oak 4  45 

White  beech 3  25 

Black  walnut 3  25 

Black  birch 3   15 

Hard  maple 3  oo 

White  elm 2  90 

Red  cedar 2  08 

Wild  cherry 2  75 

Soft  maple 2  70 

Yellow  pine 2  70 

Chestnut 260 

Butternut 2  55 

White  birch 2  40 

White  pine 2  10 

Experiments  on  combustion,  conducted  by  MM.  Scheurer- 
Kestner  and  Meunier-Dollfus,*  indicate  that  the  method  em- 
ployed for  determining  the  heating  power  of  fuel,  from  its 
analysis,  is  not  correct.  A  satisfactory  explanation  of  this 
difference  has  not  been  given.  The  heating  effect  may  depend 

*  Bulletin  de  la  Socitte  Industrielle  de  Mulhouse,  1868,  1869, 


108 


THE   STEAM-BOILER. 


on  the  state  in  which  the  carbon  exists  in  the  coal ;  and  that 
although  the  calorific  effect  of  the  combustion  of  charcoal  has 
been  determined,  it  may  be  higher  in  the  case  of  other  forms 
of  carbon.* 

Mr.  G.  H.  Babcock  gives  the  following  tables  as  representa- 
tive of  familiar  practice : 


A  T  r» 

HIGHEST 

AIR 

0  — 

TEMPERATURE  OF 

THEORETICAL 

ATTAINABLE 

K.E— 

COMBUSTION. 

VALUE. 

VALUE  UNDER 

QUIRED. 

BOILER. 

"o 

.c'E, 

i'S 

Cfl 

fcd 

k'g.o 

6"o  rt 

KIND  OF 
COMBUSTIBLE. 

11 

O  ^ 

|h 

§f 

SI 

S^H 

l|| 

filL 

V 

^V 

i 

•  o 

§1 

.C  ji» 

Pg 

i=l 

5^ 
21 

ii! 

HHU 

c-J 

pi! 

>       *m 

ttzS 

c 
|u 

If 

1^ 

•8£ 

"I  o 

•S3 

5fw 

.C.C 

^=  v.h 

r  «§• 

£l^ 

5H:i 

""  O  rt  o 

^2 
,gfi 

.-s|^°8 

^o<3 

S"5^ 

c 

£ 

^ 

£ 

£ 

5 

c 

£ 

J 

Hydrogen  

36.00 

5,750 

3,860 

2,860 

1  ,940 

62,032 

64.20 

Petroleum 

5,050 

2,710 

1,850 

21,000 

21.74 

18.55 

19.90 

Carbon  — 

Charcoal  ) 

Coke  V 
AnthraciteC'l  ) 

12.13 

4,580 

3,215 

2,440 

1,650 

14,500 

15.00 

13-30 

14.14 

Coal- 

Cumberland  ..  . 
Coking  bitumi- 

12.06 

"•73 

4,900 

3,360 
3,520 

2,550 
2,680 

1,730 

1,  810 

15.370 
15,837 

15.90 
16.00 

14.28 
14-45 

15.06 
15-19 

nous. 

Cannel  

11.80 

4,850 

3,330 

2,540 

1,720 

15,080 

15.60 

14.01 

14.76 

Lignite 

Q-  3^ 

4.600 

1   670 

II    7^1^ 

10  78 

Peat— 

' 

,  90 

tfWyv 

1  1,/4j 

' 

1U.  /O 

•4 

Kiln-dried  

7.68 

4-47° 

3,140 

2.420 

1,  660 

9,660 

10.00 

8.92 

9.42 

Air-dried,  25  p.  c. 

water  
Wood— 

5-76 

4,000 

2,820 

2,240 

1,550 

7,000 

7-25 

6  41 

6.78 

Kiln-dried  

6.00 

4,080 

2,910 

2,260 

1,530 

7,245 

7-50! 

6.64 

7  02 

Air-dried,  20  p.c. 

water  ... 

4.80 

3,700 

2,670 

2,100 

1,490 

5,6oo 

5.80 

4.08 

4-32 

The  above  table  gives  the  air  required  for  complete  com- 
bustion, the  temperature  attained  with  different  proportions  of 
air,  the  theoretical  value,  and  the  highest  practically  attainable 
value  under  a  steam-boiler,  assuming  that  the  gases  pass  off  at 
320°,  the  temperature  of  steam  at  75  Ibs.  pressure,  and  the  in- 
coming air  at  60° ;  also,  that  with  chimney  draught  twice,  and 
with  forced  blast  only,  the  theoretical  amount  of  air  is  required 
for  combustion. 

The  effective  value  of  all  kinds  of  wood  per  pound,  when 


*  M.  L.  Gruner,  Engineering  and  Mining  Journal,  xviii. 


THE   FUELS  AND    THEIR   COMBUSTION. 


199 


dry,  is  substantially  the  same.     The  following  are  the  weights 
on  other  authorities  of  different  woods  by  the  cord  : 

KIND  OF  WOOD.  Weight. 

Hickory,  shell-bark 4,469 

"          red  heart 3,705 

White  oak 3,821 

Red  oak 3,254 

Beech 3, 126 

Hard  maple 2,878 

Southern  pine 3,375 

Virginia  pia^.  .....      .  t 2,680 

Spruce *      2,325 

New  Jersey  pine 2,137 

Yellow  pine 1,904 

White  pine -  868 

The  following  table  of  American  coals  has  been  compiled 
from  various  sources : 


STATE. 

COAL. 

KIND  OF  COAL. 

Per  Cent  of 
Ash. 

THEORETICAL  VALUE— 

In  Heat  Units. 

In  Pounds 
of  Water 
Evaporated. 

Anthracite 

3-49 
6.13 
2.90 
15.02 
6.50 
10.77 
5-00 
5-6o 
9-50 
2-75 

2.OO 
14.80 
7.OO 
5-20 
5.60 
5-50 
2.50 

.  5-66 
6.00 
13.98 
5-oo 
9-25 
4-50 
4-50 
3-40 

14,199 

13,535 
14,221 

13,143 

13,368 

13,155 
14,021 
14-265 
12.324 
I4-391 
15,198 
13,360 
9.326 
13.025 
13,123 
12,659 
13.588 
14.146 
13.097 
12,226 
9,215   • 
13-562 
13,866 
12,962 

n,55i 
20,  746 

14.70 
14.01 
14.72 
13.60 
13.84 
13.62 

I4-5I 
14.76 

12-75 
14.89 
16.76 
13.84 

9-65 
13.48 
13.58 
13.10 
14.38 
14.64 
I3-56 
12.65 

9-54 
14.04 

14-35 
I3-4I 
11.96 
21.47 

M 

Cannel 

Semi  -bituminous 

Stone's  Gas  

Kentucky    .... 

.  .  .Brown  
.   Caking  

M 

,, 

Lignite    

Mercer  County 

,, 

.    Montauk       

Indiana  

.  .Block  

Caking 

4< 

Cannel    

Maryland  

.  .  .Cumberland  

\rkansas 

Lififnite 

Colorado     .  .    .  . 

« 

Texas 

<  < 

Washington  Ter. 
Pennsylvania 

M 

Petroleum 

2OO 


THE   STEAM-BOILER. 


Mr.  D.  K.  Clark  thus  assigns  the  several  portions  of  the 
heat  of  combustion  of  good  coke,  as  burned  in  the  locomotive  :* 


Making  steam 10,920  B.  T.  U. 

Loss  at  smoke-stack 2,316         " 

Ash  and  waste 764         ' ' 


73  per  cent. 
16.5  " 

5-5  " 


14,000  B.  T.  U.   100  per  cent. 

and  concludes  that  combustion  in  the  furnace  of  the  locomotive 
may  be,  and  often  is,  practically  perfect,  and  anticipates  that 
economy  in  the  formation  of  steam  will  only  be  improved  by 
utilizing  heat  now  wasted  at  the  chimney.  The  usual  maxi- 
mum evaporation  is  about  8  times  the  weight  of  coke  used 
• — a  low  figure,  which  is  mainly  due  to  the  comparatively  small 
proportion  of  heating-surface  adopted.  The  nearer  the  compo- 
sition of  the  fuel  approaches  that  of  coke,  the  better,  as  a  rule, 
the  economical  effect.  Coal  gives,  as  an  average,  about  two 
thirds  the  effect  of  coke,  as  customarily  burned  ;  and  its  value 
may  be  fairly  approximated,  the  composition  being  known,  by 
assuming  the  carbon  to  be  the  only  useful  constituent. 

ORDINARY  CALORIFIC    VALUES  AS  COMPARED   WITH  GOOD    BITUMINOUS 

COAL. 

Lbs.  Coal. 

I  cord  (3.62  cubic  metres)  of  seasoned  hickory  or  hard  maple 2,000 

i     "         "                                                    white  oak  1,750 

i     "         "             "                                      beech,  red  or  black  oak 1,500 

i     "         "             "                         "           poplar,  chestnut,  or  elm 1,000 

i     "         "             "                         "           soft  pine. 960 

85.  Analyses  of  Ash. — The  following  analyses  represent 
the  character  of  ashes  of  anthracite  and  bituminous  coals. 

They  may  be  taken  as  examples  simply,  since  the  ash  of 
coal  intended  for  metallurgical  purposes  should  invariably  be 
examined  before  taking  the  fuel  for  any  important  work. 

ANALYSES   OF    ASH. 


Specific 
Gravity. 

Tolor 
of  Ash. 

Silica. 

Alum- 
ina. 

Oxide 
Iron. 

Lime. 

Mag- 
nesia. 

Loss. 

Acids 
S.&P. 

Pennsylvania  Anthracite  
Bituminous  
Welch  Anthracite      

•  5*9 

•372 

Reddish 
Buff. 
Gray. 

45  6 
76.0 

42.75 

21  .OO 
44-8 

9-43 
2.60 

1.41 

12.  0 

o-33 
trace 

0.48 
0.40 

2.97 

Scotch  Bituminous  

.26 

37.6 

52.O 

3-7 

i  .  i 

5.02 

~TT  6 

5.8 

23.7 

2.6 

£  8 

Railway  Machinery,  p.  122. 


THE  FUELS  AND    THEIR   COMBUSTION.  2OI 

Where  the  difference  between  two  coals  lies  principally  in 
their  relative  percentages  of  ash,  the  comparison  is  made  in  the 
manner  about  to  be  described. 

The  anthracites  contain  so  little  other  combustible  matter, 
that,  as  shown  by  Professor  Johnson,*  their  calorific  value  is 
proportional  very  nearly  to  the  percentage  of  contained  carbon. 

86.  The  Commercial  Value  of  Fuels  is  somewhat  modi- 
fied by  the  depreciation  produced  by  presence  of  non-combus- 
tible matter  ;  this  modification  occurs  in  the  following  ways  : 

(1)  A    certain    amount  of  carbon   is  required    to  heat  the 
whole  mass  to  the  temperature  of  the  furnace.     Of  this  a  large 
part  is  lost.     It  follows,  therefore,  that  a  coal  containing  a  cer- 
tain small  quantity  of  combustible  would  have  no  calorific  value, 
and  consequently  would  be  worthless  in  the  market. 

(2)  The  presence  of   a   high    percentage    of   ash  in  a  fuel 
checks  combustion   by  its  mechanical   mixture  with   the   com- 
bustible portion  of  the  coal.     A  coal  will,  hence,  have  no  com- 
mercial value  when  the  proportion  of  refuse  reaches  a  limit  at 
which  combustion  becomes  impossible  in  consequence  of  this 
action. 

(3)  The  cost  of  transportation  of  ash  being  as  great  as  that 
of  transporting  the  combustible,  the   consumer  paying  for  ash 
at  the  same  rate  as  for  the  carbon,  and  also  being  compelled  to 
go  to  additional  expense  for  the  removal  of  ash  ;  these  facts 
also  determine  a  limit  beyond  which  an  increased  proportion  of 
ash  renders  the  fuel  valueless. 

(4)  The    determination  of  the   financial    losses    due    to  in- 
creased wear   and  tear  of  furnaces  and  boilers,  of   incidental 
losses  due  to  inequality  or  insufficiency  of  heat-supply,  and  to 
the  many  other  direct  and  indirect  charges  to  be  made  against 
a  poor  fuel,  also  indicate  a  limit  which  has  a  different  value  for 
each  case,  but  which,  in  most  cases,  is  difficult  of  even  approxi- 
mate determination.     The  determination  of  the  minimum  pro- 
portion of  combustible,  under  the  first  case,  is  made  as  follows, 
assuming  this  heat  to  be  entirely  wasted  : 

(a)  The  specific  heat  of  ash  is  usually  nearly  0.20.     Let  X 


*  Report  to  the  Navy  Department  on  American  Coals. 


2O2  THE   STEAM-BOILER. 

represent  the  percentage  of  ash  which  is  sufficient  to  render  the 
coal  valueless.  Then,  since  each  pound  of  carbon  has  a  heat- 
ing-power of  14,500  British  thermal  units  (3625  calories),  14,500 
(100  —-X)  =  A,  represents  the  available  heat  of  a  unit  in 
weight  of  the  fuel ;  100  X  0.20  X  3000°  =  B,  represents  the 
heat  required  to  raise  this  same  amount  of  coal  to  a  temperature 
equal  to  that  of  the  furnace,  which  is  here  assumed  at  3000° 
Fahr.  (1633°  Cent.)  above  the  surrounding  atmosphere. 

Since  these  quantities  A  and  B  are  equal :  14,500  (100  —  X) 
=  loo  X  0.2  X  3000°,  and  X '  •=.  96  per  cent. 

The  minimum  quantity  of  fuel  permissible  is,  therefore, 
four  per  cent,  where  the  first  consideration  only  is  taken  into 
the  account. 

(b)  The  influence  of  the  second  condition  is  at  present  not 
determinable  in  the  absence  of  experiment. 

(c)  The  cost  of  transportation  of  ash  to  the  consumer,  as  a 
part  of  the  fuel,  is  not  taken  in  the  determination  of  its  value 
to  him.     The  removal  of  ash  is  a  tax  upon  the  consumer  which 
may  be  considered  as  the  equivalent   of  the  loss  of  a  certain 
weight  of  combustible  received.     Since  this  cost  fluctuates  with 

o 

the  market  value  of  coal,  and  since  its  amount  is  determined  by 
the  same  causes,  it  is  easy  to  make  the  statement  in  that  form. 
This  cost  is  about  ten  per  cent  of  the  value  of  coal,  weight  for 
weight,  and  is  therefore  assumed  at  ten  per  cent  of  the  propor- 
tion of  ash  found  in  the  coal. 

(d)  The  losses,  direct  and  indirect,  coming  under  the  fourth 
head,  vary  greatly,  and  are  sometimes  very  serious.     An  ap- 
proximate   estimate  for  an   average  example  is  taken,  and  is 
considered  to  be  equal,  at    least,  to  a  percentage  of  the  total 
value  of  coal,  in  utilizable  carbon,  which  equals  one  half  the 
percentage  of  ash.     Comparing  two  anthracites,  which  we  will 
suppose  to  contain,  respectively,   fifteen    and    twenty-five  per 
cent  ash,  eighty-five  and  seventy-five  per  cent  carbon,  the  first 
being  a  well-known  standard  coal,  selling  in  the  market  at  six 
dollars  per  ton  (1016  kilogrammes),  we  may,  using  this  system 
of  charging  losses  against  equivalent  values  in  combustible  car- 
bon, determine   the  proper  commercial  value  of  the  second 
kind. 


THE  FUELS  AND    THEIR   COMBUSTION.  2O$ 

First  Example. — From  the  85  per  cent  carbon  : 

Deduct  for  heating  to  furnace  temperature 0.040 

"         "    transportation  of  refuse  10  per  cent  of  15 0.015 

"         "    other  losses  50  per  cent  of  15 0-075 


Total 0.130 

leaving  valuable  and  available  carbon  85  —  13  =  72  per  cent. 
Second  Example. — From  the  75  per  cent  carbon : 

Deduct  for  heating  to  furnace  temperature 0.040 

"         "    removal  of  ash  10  per  cent  of  25 0.025 

•'         "    sundry  losses  50  per  cent  of  25 o.  125 

Total 0.190 

leaving  valuable  available  carbon  75  —  19  =  56  per  cent. 

Finally,  if  $6.00  is  paid  for  72  percent  available  combustible, 

for  56  per  cent  we  should  pay —  $4-66f . 

Third  Example. — Taking  a  third  example,  in  which  the  fuel 
contains  the  exceptionally  large  proportion  of  30  per  cent  ash, 
we  should,  by  similar  method,  proceed  as  follows,  deducting 
from  the  seventy  per  cent  carbon  as  before  the  estimated 
charges  against  it : 

Deduct  for  heating 0.040 

"         "    removal  of  ash  10  per  cent  of  30. 0.030 

"         "    sundry  expenses  50  per  cent  of  30 o.  150 

Total 0.220 

leaving   available  carbon,  70  —  22  =  48  per  cent,  which  would 
be  worth  - — - —  =  $4.00. 

Had  the  first  coal  had  a  market  value  of  seven  dollars  per 
ton,  the  second  and  third  would  have  been  worth,  respectively, 
$5.44^  and  $4.66$. 

Expressing  this  operation  by  symbols,  if  V  represents  the 
value  of  the  fuel  in  percentage  of  pure  carbon,  and  A  equal  the 
percentage  of  ash,  V  •=•  0.96  —  i.6oA. 

This  method  is  evidently  largely  empirical,  and  its  results 


2O4  THE   STEAM-BOILER. 

arc  but  approximate.  It  is,  however,  simple  and  easily  applied, 
and  will  often  be  found  of  use  in  the  absence  of  more  precise 
means  of  determination. 

The  kind  and  quality  of  fuel  employed  in  the  production  of 
steam  for  commercial  purposes  is  often  determined  by  condi- 
tions quite  independent  of  the  special  quality  of  the  fuel.  In 
most  cases  the  element  of  cost  is  the  controlling  one. 

Johnson,  in  his  report  to  the  Navy  Department  (1844)  on 
American  coals,  proposes  to  grade  coals  according  to — 

(1)  Their  relative  weights. 

(2)  Rapidity  of  ignition. 

(3)  Completeness  of  combustion. 

(4)  Evaporative  power  under  equal  weights. 

(5)  Evaporative  power  under  equal  bulks. 

(6)  Evaporative  power  of  combustible  matter. 

(7)  Freedom  from  waste  in  burning. 

(8)  Freedom  from  tendency  to  form  clinker. 

(9)  Maximum  evaporative  power  under  equal  bulks. 

(10)  Maximum  rapidity  of  combustion. 

He  found  it  impossible  to  select  any  one  coal  which  could 
be  placed  first  in  all  these  qualities  or  to  attach  equal  impor- 
tance to  all.  For  steam  navigation  he  attaches  most  impor- 
tance to  the  fifth,  "  the  evaporative  power  for  equal  bulks,"  as 
stowage-space  is  supremely  important  in  steam  navigation. 
With  the  fifth  he  combines  the  eighth  and  tenth,  viz.,  "  free- 
dom from  clinker"  and  "  maximum  rapidity  of  action."  Ameri- 
can coals  are  usually  superior  to  foreign  coals. 

87.  Good  Furnace  Management,  to  secure  maximum 
heat-supply  from  the  unit  weight  of  fuel,  is  evidently  as  essen- 
tial to  economy  and  efficiency  of  steam  production  as  choice  of 
proper  fuels. 

In  the  management  of  the  furnace  the  effort  should  be 
made  to  secure  the  best  conditions  for  economy,  and  as  nearly 
as  possible  perfect  uniformity  of  those  conditions.  The  fuel 
should  be  spread  over  the  grate  very  evenly,  and  the  tendency 
to  burn  irregularly,  and  especially  into  holes  or  thin  spots, 
should  be  met  by  skilful  "  firing,"  or  "  stoking"  as  it  is  also 
termed,  at  such  intervals  as  may  by  experience  be  found  best. 


THE   FUELS  AND    THEIR    COMBUSTION.  20$ 

The  smaller  the  coal,  where  anthracite  is  used,  the  thinner 
should  be  the  fire  ;  the  stronger  the  draught  the  thicker  the 
bed  of  fuel,  of  whatever  kind.  With  too  thin  a  fire,  the  dan- 
ger arises  of  excess  of  air-supply ;  with  too  heavy  a  fire,  carbon 
monoxide  (carbonic  oxide)  may  be  produced.  In  the  former 
case  combustion  will  be  complete,  but  the  heat  generated  will 
be  distributed  throughout  the  diluting  excess  of  air,  and  thus 
rendered  less  available,  and  the  efficiency  of  the  furnace  will  be 
correspondingly  reduced  ;  while  in  the  latter  case  a  loss  arises 
from  incomplete  combustion,  and  waste  takes  place  by  the 
passage  of  combustible  gas  up  the  chimney.  The  second  is  the 
less  common  cause  of  loss  of  the  two,  but  both  are  liable  to 
arise  in  almost  any  boiler,  and  we  may  even  have  both  losses 
exhibited  in  the  same  boiler  and  at  the  same  time.  Successful 
working  demands  a  very  perfect  mixture  of  the  combustible 
with  the  supporter  of  combustion,  and  should  this  not  be 
secured,  serious  waste  will  take  place. 

The  appearance  of  smoke  at  the  chimney-top  is  not  always 
indicative  of  serious  loss,  nor  is  its  non-appearance  always  proof 
of  complete  combustion.  With  soft  coals  and  other  fuels  con- 
taining the  hydrocarbons  some  smoke  usually  accompanies 
the  best  practically  attainable  conditions ;  anthracites,  charcoal, 
and  coke  never  produce  true  smoke.  Attempts  to  improve 
the  efficiency  of  a  heat-generating  apparatus  by  "  burning  the 
smoke"  usually  fail  by  introducing  such  an  excess  of  air  as  to 
cause  a  loss  exceeding  that  before  experienced  from  the  forma- 
tion of  smokei  Thorough  intermixture  of  a  minimum  air-supply 
with  the  gases  distilled  from  the  fuel  is  the  only  means  of  at- 
taining high  efficiency. 

In  firing,  or  stoking,  especial  care  should  be  taken  to  see 
that  the  sides  and  corners  of  the  grate  are  properly  attended 
to.  Regulation  of  the  fire  is  best  secured  by  the  careful  ad- 
justment of  the  damper.  The  manipulation  of  the  furnace 
doors  for  this  purpose  is  likely  to  cause  waste.  Liquid  fuels 
are  especially  liable  to  waste  by  excessive  air-supply,  and  gas- 
eous fuel  exhibits  a  peculiar  liability  to  the  opposite  method 
of  loss  ;  both  should  be,  if  possible,  even  more  carefully  handled 
than  any  solid  fuels. 


206  THE   STEAM-BOILER. 

88.  The  Fuels,  Boiler,  and  Furnace  must  be  adapted 
each  to  the  others  very  carefully,  if  the  best  results  are  to  be 
attained.  Soft,  free-burning  fuels  demand  a  different  form  of 
grate,  as  well  as  different  air-distribution  and  furnace  manage- 
ment, from  the  hard  and  slow-burning  combustibles.  The 
form  and  size  of  furnace,  the  extent  and  kind  of  heating-sur- 
face, and  the  type  of  boiler  even,  all  influence  the  total  effi- 
ciency of  steam  generation.  Tubular  boilers  have  small  flues  or 
tubes,  and  are  better  fitted  for  use  with  anthracite  coal  and 
with  coke  or  other  fuels  burning  with  little  flame  ;  while  larger 
tubes  or  flues  are  better  adapted  for  use  with  the  bituminous 
and  other  soft,  long-flaming  combustibles.  It  thus  happens,  for 
example,  that  a  locomotive  using  anthracite  coal,  another  en- 
gine burning  bituminous  coal,  and  a  coke-burning  engine,  all 
have  different  proportions  of  boiler. 


CHAPTER   IV. 

HEAT— PRODUCTION  ;  MEASUREMENT  ;  TRANSFER  ;  EFFICIENCY 
OF  HEATING-SURFACE. 

89.  The  Nature  of  Heat,  long  debated  among  men  of 
science,  has  in  the  course  of  the  last  century  become  well 
determined.  Heat  consists  in  the  vibrations  of  the  molecules 
of  which  bodies  are  composed,  and  is  a  form  of  energy.  This 
energy,  although  actually  kinetic,  being  molecular  is  often 
taken  to  be  potential  or  latent.  The  two  forms  in  which 
energy  is  stored,  when  heat  is  communicated  to  any  substance, 
are  "sensible  heat,"  of  which  the  intensity  is  exhibited  by  the 
thermometer,  and  which  is  measured  in  quantity  by  the 
various  methods  of  calorimetry ;  and  "  latent  heat,"  which  is 
not  detected  or  measurable  as  heat,  and  which  in  fact  does  not 
exist  as  heat,  but  has  been  transformed  into  the  true  potential 
energy  of  changed  physical  state  and  altered  molecular  rela- 
tions :  it  is  manifested  by  a  change  of  volume  in  the  body 
affected. 

Thus  all  masses,  of  whatever  kind,  composition,  or  form, 
when  heated  increase  in  temperature  and  are  altered  in  vol- 
ume, and  the  sum  of  the  heat-energy  producing  the  change  in 
temperature  and  the  potential  energy  measured  by  the  prod- 
uct of  the  change  of  volume  and  the  total  intensity  of  the 
forces,  internal  and  external,  resisting  that  change  measures 
the  total  heat  transferred  to  effect  the  physical  changes  noted. 
The  sensible  heat  retains  its  original  form  ;  the  latent  heat,  so- 
called,  is  no  longer  heat  at  all,  but  may  be  retransformed  and 
may  again  appear  as  heat  on  reversing  the  first  operation  of 
transfer.  In  solids,  by  far  the  greater  part  of  the  heat  received 
remains  sensible,  and  takes  effect  in  producing  change  of  tem- 
perature ;  in  the  transformation  of  the  solid  into  liquid  by 
fusion  all  heat  absorbed  becomes  latent,  and  produces  ex- 


2O8  THE   STEAM-BOILER. 

pansion  of  volume ;  in  heating  the  liquid  the  heat  is  employed 
mainly  in  elevation  of  temperature,  but  in  part  in  doing  work 
with  the  result  of  transformation  into  latent  heat.  During 
vaporization  at  any  fixed  temperature  all  heat  is  disposed  of 
in  causing  change  of  volume,  and  this  is  known  as  the  "  latent 
heat  of  evaporation,"  or  of  vaporization  ;  while  in  the  expan- 
sion of  vapors  and  gases  the  increase  of  volume  continues  to 
be  comparatively  large  in  amount,  and  the  "  latent  heat  of  ex- 
pansion" is  a  correspondingly  large  proportion  of  the  total, 
and  is  especially  large  in  vapors,  such  as  steam,  which  have 
great  internal  potential  energy  due  to  the  action  of  powerful 
molecular  attractive  forces.  The  heat-energy  demanded  to 
make  steam  in  the  boiler  is  thus,  at  ordinary  temperatures,  ten 
times  greater  than  that  required  to  overcome  the  external 
pressure  measured  by  the  steam-gauge. 

90.  Production  of  Heat  by  Combustion  and  other  meth- 
ods involves,  in  all  cases,  the  expenditure  of  an  equivalent 
amount  of  energy  in  some  transformable  shape. 

The  original  source  of  all  heat-energy  is  found  far  back  of 
its  first  appearance  in  the  steam-boiler.  It  had  its  origin  at 
the  beginning,  when  all  Nature  came  into  existence.  After 
the  solar  system  had  been  formed  from  the  nebulous  chaos  of 
creation,  the  glowing  mass  which  is  now  called  the  sun  was  the 
depository  of  a  vast  store  of  heat-energy,  which  was  thence 
radiated  into  space  and  showered  upon  the  attendant  worlds 
in  inconceivable  quantity  and  with  unmeasured  intensity. 
During  the  past  life  of  the  globe  the  heat-energy  received 
from  the  sun  upon  the  earth's  surface  was  partly  expended  in 
the  production  of  great  forests,  and  the  storage,  in  the  trunks, 
branches,  and  leaves  of  the  trees  of  which  they  were  composed, 
of  an  immense  quantity  of  carbon,  which  had  previously  ex- 
isted in  the  atmosphere,  combined  with  oxygen,  as  carbonic 
acid.  The  great  geological  changes  which  buried  these  forests 
under  superincumbent  strata  of  rock  and  earth  resulted  in  the 
formation  of  coal-beds,  and  the  storage,  during  many  succeed- 
ing ages,  of  a  vast  amount  of  carbon,  of  which  the  affinity  for 
oxygen  remained  unsatisfied  until  finally  uncovered  by  the 
hand  of  man  Thus  we  owe  to  the  heat  and  light  of  the  sun, 


HEAT— PRODUCTION;   MEASUREMENT;   TRANSFER.     2OQ 

as  was  pointed  out  by  George  Stephenson,  the  incalculable 
store  of  potential  energy  upon  which  the  human  race  is  so 
dependent  for  life  and  all  its  necessaries,  comforts,  and  lux- 
uries. 

This  coal,  thrown  upon  the  grate  in  the  steam-boiler,  takes 
fire,  and,  uniting  again  with  the  oxygen,  sets  free  heat  in  pre- 
cisely the  same  quantity  that  it  was  received  from  the  sun  and 
appropriated  during  the  growth  of  the  tree.  The  actual  energy 
thus  rendered  available  is  transferred,  by  conduction  and  radia- 
tion, to  the  water  in  the  steam-boiler,  converts  it  into  steam,  andi 
its  mechanical  effect  is  seen  in  the  expansion  of  the  liquid  into 
vapor  against  the  superincumbent  pressure.  Transferred  from 
the  boiler  to  the  engine,  the  steam  is  there  permitted  to  ex- 
pand, doing  work,  and  the  heat-energy  with  which  it  is  charged 
becomes  partly  converted  into  mechanical  energy,  and  is  ap- 
plied to  useful  work  in  the  mill  or  to  driving  the  locomotive  or 
the  steamboat. 

Thus  we  trace  the  store  of  energy  received  from  the  sun 
and  contained  in  the  fuel  through  its  several  changes  until  it  is 
finally  set  at  work ;  and  we  might  go  still  further  and  observe 
how,  in  each  case,  it  is  again  usually  retransformed  and  again 
set  free  as  heat-energy. 

The  transformation  which  takes  place  in  the  furnace  is  a 
chemical  change;  the  transfer  of  heat  to  the  water  and  the 
subsequent  phenomena  accompanying  its  passage  through  the- 
engine  are  physical  changes,  some  of  which  require  for  their 
investigation  abstruse  mathematical  operations.  A  thorough 
comprehension  of  the  principles  governing  the  operation  of  the 
steam-boiler  can  only  be  attained  after  studying  the  phenom- 
ena of  physical  science  with  sufficient  minuteness  and  ac- 
curacy to  be  able  to  express  with  precision  the  laws  of  which 
those  sciences  are  constituted.  The  study  of  the  philosophy 
of  the  generation  and  application  of  steam  involves  the  study 
of  chemistry  and  physics,  and  of  the  new  science  of  energetics,, 
of  which  the  now  well-grown  science  of  thermo-dynamics  is  a. 
branch. 

These  sciences,  like  the  steam-engine  itself,  have  an  origin 
which  antedates  the  commencement  of  the  Christian  era;  but 
14 


210  THE   STEAM-BOILER. 

they  grew  with  an  almost  imperceptible  growth  for  many  cen- 
turies, and  finally,  only  a  century  ago,  started  onward  suddenly 
and  rapidly,  and  their  progress  has  never  since  been  checked. 
They  are  now  fully-developed  and  well-established  systems  of 
natural  philosophy.  Their  consideration  is  the  special  province 
of  works  on  the  physical  sciences  and  on  applied  mechanics. 

Combustion  is  simply  the  union  of  some  combustible  with 
oxygen ;  but  this  phenomenon  involves  both  chemical  and 
physical  operations.  The  first  operation  is  a  physical  phenom- 
enon :  it  consists  in  the  elevation  of  the  temperature  of  one 
or  both  constituents  of  the  compound  to  be  formed,  until,  by 
some  as  yet  not  clearly  understood  modification  of  their  mo- 
lecular relations,  their  chemical  affinities  come  into  play  and 
combination  takes  place.  But  this  combination  consists  in  the 
enforced  approximation  of  molecule  to  molecule,  a  relative 
motion  taking  place  of  great  rapidity,  and  work  is  thus  done 
of  considerable  amount.  The  resulting  collision  converts  this 
energy  of  molecular  motion  into  that  energy  of  molecular 
vibration  familiar  to  us  as  heat,  and  the  quantity  of  heat  so 
produced  is  the  measure  of  the  potential  energy  of  chemical 
affinity  in  which  it  has  its  origin.  With  its  development  in 
this  form  this  energy  assumes  an  available  and  manageable 
form,  and  becomes  at  once  capable  of  application  to  the  pur- 
poses of  the  engineer.  It  may  now  be  measured,  stored,  trans- 
ferred wherever  wanted,  and  finally,  as  required,  transformed 
into  mechanical  energy,  and  in  that  form  applied  to  all  kinds 
of  useful  work. 

91.  Temperatures  and  Quantities  of  Heat  are  related  to 
each  other  as  are  pressures  and  work  in  dynamics.  The  one  is 
a  factor  of  the  other,  but  the  first  is  not  a  measure  of  the 
second.  Temperature  measures  the  intensity  of  molecular 
heat-vibrations  and  the  tendency  of  heat-energy  to  transfer  it- 
self to  another  body,  very  much  as  the  pressure  or  tension  of 
a  confined  gas  or  of  steam  measures  the  tendency  to  expand. 
In  fact,  the  pressure  of  a  confined  gas  and  the  total  internal 
and  external  pressure  of  a  vapor  or  other  substance  are  directly 
and  precisely  proportional  to  the  temperature,  measured  from 
the  absolute  zero  of  heat-motion. 


HEAT— PRODUCTION;  MEASUREMENT;    TRANSFER.     211 

Quantity  of  heat  is  the  measure  of  the  energy,  whether  in 
heat-units  or  in  equivalent  mechanical  units, — thermal  units, 
calories,  or  foot-pounds, — of  the  heat  transferred  in  any  change. 
It  is  equal  to  the  product  of  the  weight  of  the  mass  affected, 
its  specific  heat  and  the  range  of  temperature  marking  the 
change. 

Temperatures  are  measured  in  either  Fahrenheit  or  centi- 
grade degrees,  and  on  either  the  common  or  the  absolute  scale. 
On  the  Fahrenheit  thermometric  scale  the  range  of  tempera- 
ture between  the  two  standards,  the  melting-point  of  ice  or  the 
freezing-point  of  water,  under  normal  atmosphere  and  pressure, 
and  the  boiling-point  of  pure  water  under  one  atmosphere,  is 
divided  into  180  equal  parts  or  degrees,  and  the  zero  is  con- 
ventionally placed  thirty-two  degrees  below  the  former  point, 
the  freezing  and  boiling  points  thus  being  found  at  32°  Fahr, 
and  212°  Fahr.,  respectively.  On  the  centigrade  thermometer 
the  range  between  the  standard  temperatures  is  made  100°,  and 
the  zero  is  taken  conventionally  at  the  lower  of  these  two  tem- 
peratures, the  freezing  and  boiling  points  being  thus  at  o°  Cent, 
and  100°  Cent.,  respectively. 

The  " absolute  scale'  of  temperatures  is  one  on  which  it  is 
sought  to  place  the  zero-point  at  the  absolute  zero  of  heat- 
motion — at  that  point  at  which  all  heat-energy  becomes  zero  and 
temperature  ceases  to  have  existence.  This  is  found  to  be  at 
very  nearly  —  461°. 2  Fahr.,  or  —  274°  Cent. ;  so  that,  on  the  ab- 
solute scale,  the  standard  temperatures  are  -f-  393°. 2  Fahr.  and 
+  573°. 2  Fahr.,  or  +  274°  Cent,  and  +  374°  Cent.  It  is  found 
that  the  scale  of  the  air-thermometer  is  sensibly  coincident 
with  the  absolute  scale,  provided  its  readings  are  made  propor- 
tional to  the  volumes  of  the  enclosed  gas  at  the  several  tern 
peratures.  Calling  T  the  temperature  on  this  scale  the  charac 

pv 
teristic  equation  -=  =  constant  is   found  correct  for  all   true 

gases,  /  and  v  being  the  pressure  and  volume  of  unity  of 
weight  at  any  assumed  temperature,  T\  hence  for  the  air-ther- 
mometer, in  which  /  is  constant,  v  oc  T. 

The  Thermal  Unit,  the  unit  by  which  quantity  of  heat  is 
measured  as  heat,  is  that  amount  of  heat-energy  which  i«  de- 


212 


THE   STEAM-BOILER. 


manded  to  raise  the  temperature  of  unity  of  weight  of  water 
from  the  temperature  of  maximum  density  to  one  degree 
above  that  point.  The  British  thermal  unit  is  measured,  cus- 
tomarily, by  the  engineer,  by  the  "  pound-degrees,"  and  quanti- 
ties of  heat  are  measured  by  the  number  of  such  thermal  units 
transferred.  The  metric  thermal  unit  or  "  calorie,"  as  it  was 
called  by  the  French  philosophers  who  first  adopted  the  metric 
system,  is  that  quantity  of  heat  which  is  required  to  raise  the 
temperature  of  one  kilogramme  of  water  one  degree  centi- 
grade,—  the  "  kilogramme-degree." 

Specific  Heat  is  the  quantity  of  heat  in  thermal  units  de- 
manded by  unity  of  weight  of  any  given  material,  as  of  water 
to  raise  its  temperature  one  degree.  When  this  heat  is  all 
sensible,  it  is  simply  called  specific  heat,  but  when  it  is  in  any 
observable  amount  latent,  as  in  expansion  of  gases,  a  distinction 
must  be  made  between  the  "  Specific  Heat  at  Constant  Vol- 
ume," which  is  the  real  specific  heat,  and  the  "  Specific  Heat 
at  Constant  Pressure,"  and  other  specific  heats  involving  more 
or  less  transformation  of  heat  in  the  performance  of  the  work 
of  expansion.  The  specific  heats  of  the  gases  are  given  in  §  78 
for  constant  pressure.  Those  of  the  solids  are  given  in  the 
following  table : 


SPECIFIC   HEATS  OF  METALS  AND  MINERALS. 


Iron 

o  II37Q  acc. 

to  Re£ 
i 

i 
i 
i 
i 
i 
i 
i 

jnault,  o.i  100 
'           0.0927 
0.0949 

Zinc  

CooDcr  . 

Brass              . 

O   OQ3QI 

0.0557 
'           0.0293 
0.0288 
0.0507 
'           0.0514 
'           0.0314 
'           0.0298 

'           0.1880 
t 
it 
t 
t 

Lead     

.  .  .  .  o  03140 

Bismuth     .  . 

.  .  .  .  o  03084 

Antimony  . 

O   O5O77 

Tin   

.    O.O5623 

Platinum      .  . 

Gold 

O  O324.4. 

Sulphur 

O    2O25Q 

Coal   

.  .  .  .    O.24III 

Coke     

.    .  .    O.2O3O7 

Graphite  .  .  . 

...  o.  20187 

Marble.. 

.  0.20080 

HEAT— PRODUCTION;   MEASUREMENT;    TRANSFER.     21$ 

Unslaked  Lime.  0.2169    according  to  Lavoisier  and  Laplace. 

Oak-wood 0.570  "  "  Mayer. 

Glass 0.19768         "  "  Regnault. 

Mercury 0.03332         "  "         " 


Laplace  and  Lavoisier  employed  the  method  by  melting ; 
Dulong  and  Petit,  the  cooling  method  ;  Pouillet,  and  recently 
also  Regnault,  the  method  by  mixture,  which  seems  to  be  the 
most  accurate  method. 

Coke,  coal,  masonry,  and  the  stones  and  earths  may  be  taken 
as  averaging  very  closely  c  =  0.20.  The  woods  range  from 
.c  —  0.50  to  c  —  0.65. 

The  specific  heat  of  the  same  material,  as  has  been  seen, 
is  not  perfectly  constant,  but  increases  as  the  temperature  in- 
creases. Thus,  according  to  Dulong  and  Petit,  the  mean  spe- 
cific heat  is  as  follows : 


Iron between  o°  and  100°,  0.1098;  between  o°  and  300°,  0.1218 

Mercury "         "  "      0.0330;         "        " 

Zinc "         "  "      0.0927;         "        " 

Copper "         "  "      0.0947; 

Platinum "         "  "      0.0335;         "        " 

•Glass '         "  "      0.1770;         "        " 


0.0350 
0.1015 
o. 1013 
o  0355 
0.190 


Regnault  found  the  ratio  of  the  specific  heats  of  the  gases 
to  be: 


( 

i 

Constant 
/olume. 

( 

1 

Constant 
'ressure. 

Air     .           .    .                       

.^66^ 

•2670 

Hydrogen     

.1667 

•}66l 

Nitrogen  

.3668 

Carbonic  Acid                                       .           .  . 

3688 

1660 

Carbonic  Oxide.  

q667 

•37]  Q 

Nitrous  Oxide   

•  1676 

?7IQ 

Cyanogen                                                                 .  . 

q82Q 

-3877 

Sulphurous  Acid     .  .    .  .        

.384-} 

•7QO7 

A  relation  between  the  specific  heat  and  the  atomic  weight 
originally  established  by  Dulong  and  Petit,  and  confirmed  by 
Regnault,  is  very  interesting.  The  product  of  the  specific 


214  THE   STEAM-BOILER. 

heats  and  the  atomic  weights  is  nearly  constant,  and  varies  only 
from  38  to  42  ;  thus  : 

C.  At.  Wts.  Products. 

For  Iron 0.11379  339-21  38.597 

"   Silver 0.05701  675.80  38.527 

"    Platinum 0.03243  1233-5  39-993 

"    Sulphur 0.20259  201.17  40.754 

92.  Thermometry  and  Calorimetry  are  the  processes  em- 
ployed by  physicists  and  engineers  in  the  quantitative  deter- 
mination of  temperatures,  and  of  quantities  of  heat  and  their 
variations.  The  instruments  employed  consist  of  the  various 
kinds  of  thermometers  and  pyrometers  for  measuring  tempera- 
tures, and  of  several  sorts  of  calorimeter,  the  form  being  deter- 
mined by  the  character  and  accuracy  demanded  by  the  work 
to  be  done. 

Thermometers  usually  consist  of  a  bulb,  commonly  of  glass, 
and  a  capillary  stem  which  the  fluid  inclosed  traverses  as  its 
volume  changes,  the  position  of  the  head  of  the  column  at 
any  moment  indicating  the  temperature  attained  by  the  instru- 
ment at  the  instant,  the  reading  being  taken  from  a  scale 
established  by  the  maker  and  standardized  by  reference  to  the 
standard  temperatures  or  by  comparison  with  another  instru- 
ment of  known  accuracy. 

Mercury  is  generally  used  in  thermometers  ranging  from 
below  the  freezing-point  up  to  about  500°  Fahr.  (260°  Cent.). 
For  the  extremely  low  temperatures  at  which  mercury  might 
freeze,  alcohol  is  used,  and  it  may  be  employed  also  for  familiar 
atmospheric  temperatures.  For  temperatures  approaching  or 
exceeding  the  boiling-point  of  mercury,  the  various  metallic 
thermometers  or  "  pyrometers"  are  used,  which  depend  for 
their  operation  upon  differences  in  the  rates  of  expansion  of 
two  metals.  Siemens'  electric  pyrometer  depends  for  its  action 
on  the  variation  of  the  resistance  of  a  conductor  of  electricity 
with  variation  of  temperature. 

The  finer  kinds  of  thermometer  used  in  the  thermometry 
of  the  engineer  are  mainly  employed  in  the  determination  of 
temperatures  of  air  and  water,  in  the  measurements  connected 


HEAT—  PRODUCTION;   MEASUREMENT;    TRANSFER.     21$ 

with  steam-boiler  trials.  They  are  always  mercurial  thermom- 
eters, and  are  made  and  standardized  with  the  utmost  possible 
accuracy  ;  those  used  in  the  calorimeters  employed  in  deter- 
mining the  character  of  the  steam  furnished  by  boilers  are  often 
graduated  to  tenths,  or  even  to  twentieths,  of  degrees.  .The 
pyrometers  used  by  the  engineer  are  commonly  constructed  of 
a  tube  inclosing  a  rod  of  a  different  metal,  the  two  secured 
together  at  one  end,  while  at  the  other  end  the  tube  carries  a 
case  and  dial,  and  the  rod  actuates  a  pointer,  through  some 
system  of  multiplying  gear.  The  tube  is  usually  of  iron,  and 
the  rod  of  brass  or  copper.  A  more  sensitive  form  is  that  in 
which  the  disposition  of  the  two  metals  is  reversed.  The 
special  forms  of  calorimeter  used  in  connection  with  boiler 
tests  will  be  described  later. 

Regnault's  and  Wiedemann's  experiments,  made  on  simple 
gases,  and  on  carbonic  oxide  which  is  formed  without  con- 
densation, proved  that  in  these  cases  the  specific  heat  between 
o°  and  200°  C.  is  constant  ;  whilst  their  experiments  on  gases 
formed  with  condensation  show  that  the  specific  heat  varies, 
the  mean  being  given  in  the  following  empirical  formulae  : 

For  CO2    =    44  gr.  C.   =    8.41  -f-  0.0053^  )  Mean  of  Regnault 
"      NO     =44       "       =    8.96  -j-  0.0028^)   and  Wiedemann. 
"     C2S4  =76       "       =  10.62  -f  0.007/,      Regnault. 
"     NH3  =    17       "       =    8.51  -f-  0.00265^,  Wiedemann. 
"     C4H4  =    28       "       =    9.42  +  o.oiis/,    Wiedemann. 


93.  The  Transfer  of  Heat  from  the  furnace  to  the  boiler 
involves  the  application  of  chemical  and  physical  principles 
which  will  be  briefly  stated  in  a  succeeding  part  of  this  chapter. 
The  production  of  heat  by  the  chemical  processes  involved  in 
construction  has  been  seen  to  be  governed  by  the  nature  of  the 
fuel,  by  the  relative  proportion  of  combustible  and  of  sup- 
porter of  combustion,  and  by  the  quantity  of  diluting  gases 
present.  The  heat,  once  produced,  is  the  more  completely 
available  as  the  temperature  of  the  products  of  combustion  is 
higher  ;  it  is  the  more  completely  utilized,  also,  as  the  arrange- 
ments for  its  transfer  are  the  more  complete  and  effective. 

The  utilization  and  the  waste  of  heat  are  dependent  upon 


2l6  THE   STEAM-BOILER. 

the  method  and  extent  of  its  transfer  to  the  absorbing  appara- 
tus, or  to  other  bodies.  The  heat  generated  in  the  furnace  of 
a  steam-boiler  is  usually  mainly  transferred  to  the  boiler  by 
radiation,  conduction,  and  convection,  partly,  often  in  some- 
what large  proportion,  to  the  chimney  and  the  outer  air  by 
convection,  and  to  some  extent  to  adjacent  objects  by  conduc- 
tion or  radiation  through  the  furnace-walls  and  the  occasionally 
opened  furnace-doors.  The  laws  and  the  extent  of  these  utili- 
zations or  wastes  are  fairly  well  understood,  and  can  be  some- 
times calculated  with  a  satisfactory  degree  of  accuracy  and 
certainty. 

The  tendency  to  transfer  heat  by  either  of  the  three  meth- 
ods, radiation,  conduction,  or  convection,  and  the  quantity  so 
transferred,  depend  upon — 

(1)  The  difference  of  temperature  between  the  source  and 
the  receiver  of  that  heat. 

(2)  The  extent  and  character  of  the  surfaces  between  which 
such  transfer  takes  place. 

(3)  The    extent    and    nature   of   the   intervening   body  or 
bodies. 

It  is  usually  assumed  that  it  is  sensibly  correct  to  take  the 
quantity  transferred,  in  any  case,  as  measured  by  the  product 
of  the  difference  of  temperature  by  a  coefficient  obtained  for 
each  substance  by  experiment. 

94.  Radiation  of  Heat  is  the  direct  transfer  of  that  form 
of  energy  from  one  body  to  another  across  intervening  space, 
the  only  medium  of  transfer  being  the  "  luminiferous  ether," 
the  waves  in  which  act  as  the  vehicles  of  transportation,  travel- 
ling at  the  rate  of  186,860  miles  (300,574,000  m.)  per  second. 
The  vibrations  of  dark,  pure  heat-waves  occur  at  the  rate  of 
400,000,000,000,000  per  second  or  less ;  those  of  greater  fre- 
quency, up  to  about  double  this  rate,  are  light-waves ;  and  still 
more  rapid  vibration  constitutes  the  actinic  or  chemical  ray. 
The  slowest  heat-rays  have  about  one  fourth  the  rate  of  the 
fastest ;  and  the  most  rapid  of  known  actinic  rays  vibrate  one 
hundred  times  as  rapidly  as  these  last.  Visibly  hot  bodies 
emit  all  kinds  of  rays.  All  bodies  are  continually  receiving 


HEAT— PRODUCTION;  MEASUREMENT;    TRANSFER.     2IJ 

and  emitting  heat-rays,  and,  according  to  Prevost's  theory  of 
exchanges,  gain  or  lose  in  total  heat  and  in  temperature  accord- 
ingly as  they  gain  by  absorption  from  surrounding  bodies  more 
than  they  yield  to  the  latter,  or  the  reverse. 

A  good  radiator  is  always  a  good  absorbent.  Any  body 
which  absorbs  a  particular  kind  of  ray  will,  when  emitting 
energy,  radiate  the  same  form.  Diathermous  substances  per- 
mit the  heat-rays  to  pass  through,  as  transparent  substances 
admit  light-rays :  but  diathermous  bodies  are  not  necessarily 
equally,  even  if  at  all,  transparent ;  and  all  substances  are  more 
•diathermous  to  some  rays  than  to  others,  while  good  absorbents 
are  not  diathermous. 

Radiation  plays  an  important  part  in  the  operation  of  the 
steam-boiler,  in  the  furnace  of  which,  when  the  fire  is  bright,  it 
is  estimated  that  usually  about  one  half  of  all  the  heat  taken 
up  by  the  generator  is  received  direct  from  the  fuel  by  radi- 
ation. 

95.  Conduction  is  the  method  of  transfer  of  heat  by  flow 
from  part  to  part  in  the  same  body,  or  from  one  to  another  of 
bodies  in  contact.  These  two  phenomena  are  not  precisely  the 
same.  The  flow  of  heat  from  a  hot  to  a  cold  body  in  contact 
depends  not  only  upon  the  conducting  power  of  the  two  sub- 
stances, but  also,  and  often  mainly,  on  the  condition  of  the 
touching  surfaces  and  the  perfection  of  their  contact.  The  rate 
of  transfer  within  any  given  material  depends  solely  on  the 
variation  of  temperature  along  the  line  of  flow,  and  on  the 
character  of  the  substance. 

Conductivity  measures  the  rate  of  flow,  or  of  transfer  of 
heat,  under  any  assumed  and  defined  conditions ;  it  is  the 
power  of  transmission  of  heat.  The  rate  of  conduction,  or  the 
conductivity,  may  be  expressed  by  the  number  of  thermal 
units  passing  across  a  surface,  or  through  an  internal  section, 
in  the  unit  of  time ;  it  is  proportional  to  the  rate  of  variation 
of  temperature  along  the  line  of  flow  and  to  the  constant  co- 
efficient denominated  the  conductivity,  or  the  coefficient  of  con- 
ductivity. Thus  the  quantity,  Q,  of  heat  passing  in  any  given 
time,  /,  is  measured  by  the  product  of  that  time  into  the  con- 


218  THE   STEAM-BOILER. 

//7"1 

ductivity,  k,  and  into    ,  ,  the  rate  of  variation  of  temperature 
with  distance  traversed,  and  area  of  section,  A, 

dT 


The  value  of  k  varies  greatly  with  different  substances,  be- 
ing comparatively  high  with  the  metals  and  very  low  with  all 
organic  materials  and  the  minerals.  Where  k  is  constant,  the 
equation  above  given  becomes 


(2) 


Where,  as  is  often  the  case,  the  thermal  resistance  instead 
of  the  conductivity  is  taken,  we  shall  have,  when  r  is  the  co- 

efficient of  resistance,  r  =  -r,  and 


and  the  following  values  of  r  are  found  by  experiment,  accord- 
ing to  Peclet,  for  x  in  inches  and  Q  in  British  thermal  units 
per  hour:* 

Gold  and  silver  ....................................  0.0016 

Copper  ...........................................  0.0018 

Iron  ..............................................  0.0043 

Zinc  .............................................  0.0045 

Lead  ----  .  .......  .  .................................  0.0090 

Stone  ...........................................  0.0716 

Brick  ............................................  o.  1500 

Where  the  plate  consists  of  laminae,  each  may  be  considered 
by  itself,  and  the  total  resistance  obtained  by  adding  together 
the  resistances  of  the  several  parts. 

*  Vide  Rankine's  Steam-engine,  p.  259. 


HEAT— PRODUCTION;  MEASUREMENT;    TRANSFER. 

The  surface  resistance  forms  so  large  a  part  of  the  total  in 
steam-boiler  practice,  that  the  formula 


may  be  conveniently  used  to  compute  the  amount  of  heat 
transferred,  a  being  taken  as  from  1 50  to  200  in  British  meas- 
ures (15  to  20  in  metric  measures),  accordingly  as  the  surfaces 
are  clean  or  not,  the  plate  being  of  iron,  with  water  on  one  side 
and  hot  gases  on  the  other. 

96.  Convection  of  Heat  occurs  by  its  communication  to 
the  particles  of  a  fluid,  and  then  by  the  flow  of  those  particles 
into  new  positions,  and  by  their  contact  with  the  receiver  of 
heat  by  the  transfer  of  that  heat  to  such  receiver.  Convection 
is  the  only  method  of  transfer  in  liquids,  since  conductivity  is 
not  appreciable,  and  it  is  only  by  its  transportation  by  means 
of  currents  that  it  can  be  transferred  at  all.  A  good  circulation 
is  therefore  essential  to  rapid  transfer,  and  the  rate  of  transfer 
is  thus  in  a  sense  proportional  to  the  efficiency  of  circulation. 
Thus  the  efficiency  of  a  steam-boiler  is  dependent  upon  the 
effectiveness  of  its  circulation,  as  well  as  upon  the  extent  and 
conductivity  of  its  heating-surfaces.  A  quiescent  mass  of  water 
or  of  gas  is  incapable  of  transferring  heat,  and  that  element  can 
only  pass  such  a  mass  by  penetrating  it  as  radiated  energy,  its 
vehicle  being  the  ether,  which  pervades  all  diathermic  sub- 
stances. Heat  applied  to  the  surface  of  still  water  does  not 
pass  downward  at  all  or  in  any  direction  by  real  conduction  ; 
applied  at  one  side  or  at  the  bottom  of  the  mass,  currents  are 
at  once  set  up,  by  means  of  which  a  rapid  upward  transfer  of 
heat  may  take  place.  Thus  convection  invariably  produces 
transportation  of  heated  particles,  and  transfer  of  heat,  from 
the  source  of  heat  to  a  receiver  of  heat,  or  a  refrigerator,  at  a 
higher  level.  For  best  effect  the  heat  must  in  all  cases  be 
applied  at  the  lowest  part  of  the  fluid  mass.  These  facts  and 
deductions  are  equally  true  of  liquids  and  gases,  the  latter 
being  even  more  perfect  non-conductors  than  the  former. 


22O  THE   STEAM-BOILER. 

Condensation  of  steam  and  other  vapors  by  contact  with 
cooling  surfaces  at  temperatures  below  those  of  vaporization 
always  occur  by  a  peculiar  convection,  the  circulating  or  mov- 
ing currents  of  vapor  streaming  toward  the  refrigerating  sur- 
faces, these  streams  having  their  origin  in  the  condensation  of 
the  vapor  in  contact  with  the  latter,  and  the  formation  thus  of 
a  vacuous  space  into  which  they  are  driven  by  the  elasticity  of 
the  fluid.  A  continuous  condensation  and  steady  flow  is  pro- 
duced, and  is  sustained  as  long  as  these  conditions  persist. 
This  operation  is  the  most  rapid  of  all  known  methods  of  con- 
vection or  of  transfer  of  heat,  the  mobility  of  the  vapor  per- 
mitting the  most  rapid  movement  of  its  currents,  and  its  instan- 
taneous condensation  preserving  a  constant  head  which  forces 
the  fluid  in  the  direction  of  the  condensing  surface  on  which  it 
is  converted  into  a  liquid  of  comparatively  small  volume  and 
capable  of  prompt  and  complete  removal. 

97.  The  Transfer  of  Heat  in  Boilers  is  due  to  convec- 
tion largely.  It  is  obvious  that  where  transfer  of  heat  takes 
place  from  one  fluid  to  another  through  the  sides  of  a  contain- 
ing vessel,  as  in  the  steam-boiler,  or  the  surface-condenser  of 
the  marine  steam-engine,  the  two  fluids  should  be  so  circum- 
stanced that  their  currents  should  flow  in  opposite  directions, 
the  heating  or  the  cooled  fluid  entering  on  the  heating-surface 
of  the  boiler  or  other  vessel  at  its  point  of  maximum  tempera- 
ture, and  passing  off  at  the  coolest  part ;  while  the  coo'ing  or 
heated  fluid,  the  receiver  of  heat,  should  come  into  contact 
with  the  separating  sheet  of  metal  at  its  coldest  part  and  pass 
off  at  the  hottest.  In  the  steam-boiler  the  feed-water  should 
enter  at  that  part  at  which  the  furnace-gases  are  entering  the 
chimney-flue,  and  should  circulate  toward  the  furnace.  In  the 
surface-condenser  the  condensing  water  should  enter  near 
where  the  water  of  condensation  is  taken  away  by  the  pumps, 
and  should  issue  near  the  point  at  which  the  steam  enters.  It 
is  further  evident  that  in  the  latter  case,  other  things  being 
equal,  that  disposition  of  apparatus  which  permits  most  rapid 
and  complete  removal  of  the  drops  and  streams  of  water  of 
condensation  from  the  cooling  surfaces,  so  as  to  give  at  all 
times  the  maximum  possible  area  of  effective  surface,  will  pro- 


EFFICIENCY  OF  HEATING-SURFACE.  221 

duce  the  highest  efficiency.  This  has  been  found  practically  of 
essential  importance  in  the  design  and  construction  of  such 
condensing  apparatus. 

Feed-water  heaters  for  the  above-stated  reasons  are  placed 
in  the  chimney-flue,  while  superheaters  are  sometimes  placed 
in  the  furnace.  Considerations  of  convenience  and  economy, 
however,  oftener  compel  the  designing  engineer  to  place  the 
latter  at  the  exit  of  the  furnace  gases  from  the  boiler  and 
between  the  latter  and  the  feed-\vater  heater.  As  a  rule,  how- 
ever, the  rapidity  and  completeness  of  the  circulation  of  the 
waters  in  a  well-designed  boiler  are  such  that  the  point  of 
introduction  of  feed-water  is  a  matter  of  minor  importance,  so 
far  as  the  boiler  itself  is  concerned  ;  and  the  engineer  usually 
seeks  to  enter  the  feed  in  such  a  manner  as  shall  evade  risk  of 
injury  by  irregular  strains  due  to  excessive  differences  of  tem- 
perature in  its  different  parts.  The  mass  of  water  in  a  good 
boiler,  freely  steaming,  may  be  assumed  to  have  substantially 
uniform  temperature,  and  only  the  furnace  gases  need  be  con- 
sidered as  flowing  in  definite  paths  with  varying  temperature. 
The  use  of  the  "  counter  current,  as  it  is  called,  is  better  illus- 
trated practically  in  the  case  of  the  condenser. 

Experience  shows  that  the  thickness  of  the  intervening 
plate  has  practically  no  important  influence,  as  a  rule,  on  the 
efficiency  of  transfer.  Thick  furnace-flues  and  thin  tubes  in 
the  steam-boiler  seem  about  equally  effective ;  and  the  Author 
has  known  cast-iron  condenser-tubes  to  work  practically  with 
the  same  efficiency  as  the  thin  brass  tubes,  of  one  quarter  their 
thickness,  customarily  employed.  It  should  be  stated,  how- 
ever, that  sheets  of  iron  or  steel  in  the  furnaces  of  boilers,  or 
in  flues  where  exposed  to  nearly  furnace  temperatures,  are 
liable  to  injury  by  "  burning,"  if  very  thick,  and  especially. if 
the  laps  of  their  seams  are  so  exposed.  In  some  cases  the  law 
forbids  the  use  of  heavy  plates  in  furnace-flues  or  parts  exposed 
to  flame. 

98.  Efficiency  of  Heating  or  Cooling  Surface  measures 
the  ratio  of  actual  amount  of  heat  transmitted  across  such  sur- 
face to  the  total  quantity  available  for  such  application ;  in 
steam-boilers  it  is  the  ratio  of  the  quantity  of  heat  utilized  in 


222  THE    STEAM-BOILER. 

heating  and  vaporizing  the  fluid  to  the  total  which  is  produced 
by  the  furnace,  the  unutilized  heat  being  wasted  by  conduction 
and  radiation  to  other  bodies,  or  sent  up  the  chimney.  An 
expression  was  found  by  Rankine,  based  upon  equation  (4)  of 
article  95,  which  has  been  found  to  give  very  satisfactory  re- 
sults when  properly  used  in  application  to  the  ordinary  work  of 
steam-boilers.  This  expression  may  be  derived  as  below. 

Let  w  be  the  weight  of  furnace-gases  discharged  per  hour, 
T  —  t  the  difference  between  the  temperatures  of  gas  and  water 
on  opposite  sides  of  any  part  of  the  plate  on  the  elementary 
area  dS,  C  the  specific  heat  of  the  gas,  and  let  q  be  the 
quantity  of  heat  passing  across  unity  of  area  in  unity  of  time 
for  a  difference  in  temperature  T  —  /,  in  other  words,  the  "  rate 
of  conduction"  per  unit  of  area  per  hour. 

The  quantity  of  heat  transferred  across  the  area  dS  is  then 
equal  to  qdS,  and  the  fall  of  temperature  of  gas  must  be  this 
quantity  divided  by  the  product  of  the  weight,  w,  and  specific 
heat,  C,  of  the  gas  from  which  the  heat  is  derived, 


and  the  gas  flows  on  to  the  next  elementary  area  and  beyond, 
surrendering  its  heat  as  it  goes,  until  it  finally  leaves  the  ab- 
sorbing surface  and  enters  the  chimney-flue. 

If  Tv  and  Tt  are  the  initial  and  final  temperatures  of  the 
gas,  and  /  the  temperature  of  the  water  entering  the  boiler,  the 
heat  produced,  Qlt  and  that  wasted,  Qv  per  hour,  are  respec- 
tively measured  by 

ft  =  Cw(T,  -  t)  :  Q,  =  Cw(T,  -  /),  nearly;  .     .     (2) 

while  the  efficiency  of  the  heating-surface  is  measured  by  the 
ratio  of  total  heat  to  absorbed  heat  ;  or,  if  the  feed  enters  at 
atmospheric  temperature,  or  nearly  so,  by 


EFFICIENCY  OF  HEATING-SURFACE.  22$ 

The  heat   utilized,   Cw(  T,  —  T^),  is  also   equal  to  that  ab- 
sorbed and  transmitted,  qdS: 


t-T^   and    -      =          ~.      •    •    (4) 


The   value  of   q   has  been  found    to   be   well  represented 
by   equation   (4)    of   article   95,   in  which  q  —  -=-,  and  hence 

sit 

(T  —  TV 
q  =  - — ~  ;  and  thus 


dT 

- 


Assume  (T—  t)  =  x,  then 


_  -t         f>      . 

aCw      JT      (T-tf  ~  J     ' 


T 


'  aCw       TI  —  t      TI  — 
and  the  efficiency  becomes 

Tt-T, 


Then,  since 


;  -  /      5(7;  -  /)  +  i 


^  _ 

aCw  aCw 


224  THE   STEAM-BOILER. 

and 

( 7; -o- (?;-/)     7;-  7; 


7>__7;  _         5(7; -/) 
— ""  - 


If  the  total  heat  absorbed  per  hour  be  taken  as  //", 


_*\                    T"1                   *  /           \ 

,  —  /);     Tl—t  =  -7^-\  .    .    .    (io> 

/     10t  \            / 

and  a  simplified  expression, 


H 


is  obtained,  in  which  Cw  may  be  taken  as  proportional  to  the 
weight  of  air  supplied  or  of  fuel  burned,  and  H  as  proportional 
to  the  same  quantity.  Thus  if  F  is  the  weight  of  fuel  burned 
in  the  given  time,  on  unity  of  grate-area,  the  efficiency  may  be 
expressed  -as 


E- 

~ 


which  is  the  formula  sought.  A  and  B  are  constants  to  be  ob- 
tained by  experiment  for  the  special  type  of  boiler  to  be  con- 
sidered. 

When  5  and  F  represent  respectively  the  number  of  square 
feet  of  heating-surface  per  square  foot  of  grate  in  any  boiler, 
and  the  number  of  pounds  of  fuel  burned  as  the  square  foot  of 

F 
grate  per  hour,  and  R  =  ^,  the  values  of  A  and  B,  as  given  by 

Rankine,*  are  as  follows  : 

*  Steam-engine,  p.  294. 


EFFICIENCY  OF  HEATING-SURFACE. 


225 


BOILER  TYPE.  A,  B. 

Class  I.   Best  convection,  chimney  draught 0.5  i.oo 

"      2.   Ordinary   "                 "               "        0.5  0.90 

3.   Best           "           forced           "        0.3  i.oo 

"      4.   Ordinary  "                 "               "        0.3  0.95 

These  constants  are  derived  from  experience  with  good 
fast-burning  bituminous  coals;  for  anthracites  of  good  quality 
the  Author  has  usually  found  the  following  values  more  in  ac- 
cordance with  good  practice : 

BOILER  TYPE.  A.  B. 

Class  i 0.5  0.90 

2 0-5  0.80 

3 0.3  090 

4 0.3  0.85 

When  feed-water  heaters  are  used,  or  superheaters  are  em- 
ployed, their  surface  should  be  included  in  the  area  5.  The 
formula  assumes  no  loss  by  excess  of  air-supply.  Where  such 
excess  is  noted  or  anticipated,  it  may  be  allowed  for  by  increas- 
ing the  value  of  A  in  proportion  to  the  square  of  the  total 
quantity  of  air  supplied.  The  following  table  presents  values 
of  efficiency  for  a  wide  range  of  practice  : 


EFFICIENCY  OF  BOILERS. 


BITUMINOUS  COAL. 

ANTHRACITE  COAL. 

Class  of  Boiler. 

Class  of  Boiler. 

R. 

I. 

II. 

III. 

IV. 

I. 

II. 

III. 

IV. 

10 

0.16 

0.15 

0.25 

0.22 

0.14 

0.14 

0.23 

0.20 

4 

0-33 

0.31 

0-45 

0-43 

0.30 

0.28 

0.40 

0-39 

2 

0.50 

0.46 

0.62 

0-59 

0-45 

0.50 

0.56 

o-53 

I 

0.66 

0.61 

0.77 

0-73 

0.60 

0-55 

0.70 

0.66 

0.80 

o  71 

0.65 

o  81 

0-77 

0.64 

0-59 

0.73 

o.6q 

0.67 

0-75 

0.69 

0.83 

0.79 

0.67 

0.63 

0-75 

0.72 

0.50 

0.80 

0-73 

0.87 

0.83 

0.72 

0.65 

0.78 

o-75 

0.40 

0.83 

0.76 

0.89 

0.85 

0-75 

0.68 

0.80 

°-77 

0-333 

0.86 

0.80 

0.90 

0.86 

0.77 

0.72 

0.81 

0.78 

o.  167 

0-93 

0.85 

o-95 

0.90 

0.84 

0.77 

0.86 

0.81 

O.III 

0-95 

0.87 

0.97 

0.92 

0.86 

0.78 

0.88 

0.83 

These  values  have  been  found  to  agree  well  with  practice 
up  to  rates  of   combustion    exceeding  50  or  60  pounds   per 
15 


226  THE   STEAM-BOILER. 

square  foot  of  grate-surface  per  hour,  beyond  which  point  the 
efficiency  falls  off.  But  agreement  can  only  be  expected  where 
the  combustion  and  air-supply  are  in  accordance  with  the 
assumptions  on  which  the  formula  is  based. 

The  problem  of  the  designer  of  steam-boilers  often  takes 
the  form :  Required  to  determine  the  area  of  heating-surface 
needed  to  secure  a  stated  efficiency.  In  this  case  the  formula 
above  given  must  be  transformed  thus : 


E~-~~  i  +AR  A 

1  +  S 


F~  B 

-^  —  i 


03) 


04) 


from  which  expressions,  the  efficiency  aimed  at  being  given, 
the  ratio  of  heating  to  grate-surface  and  the  extent  of  heating- 
surface  may  be  computed.  As  will  be  seen  later,  the  question 
to  what  extent  efficiency  may  be  economically  carried  by  ex- 
tending heating-surface  is  one  of  the  problems  arising  in  de- 
signing boilers. 

The  Area  of  Cooling-surf  ace  demanded  to  refrigerate  liquids, 
or  to  condense  steam  or  other  vapor,  is  capable  of  somewhat 
similar  calculation.  Returning  to  the  primary  equations  of  the 
preceding  article,  we  have 

fqdS=Cl*K-Ttr), (I) 

in  which  we  may  take  7",  as  the  measure  of  the  total  heat,  per 
unit  of  weight  of  the  steam  entering  the  condenser  or  refriger- 


EFFICIENCY  OF  HEATING-SURFACE.  22/ 

ator,  and  TJ  the  temperature  of  the  water  of  condensation  at 
its  exit.     As  before, 

TidT         Ti  dT 


in  which  /  becomes  the  temperature  of  the  circulating  or  cool- 
ing water,  while  for  such  small  differences  of  temperature  we 
may  take  q  =  C(  T  —  t\  whence 


=  MCw  \oge  -=!  -  : 


(3) 


in  which  expression  the  value  of  N  may  be  taken,  for  ordinary 
steam-engine  condensers,  at  about  0.04,  rising  in  exceptional 
case  of  inefficient  apparatus  to  o.io,  and  falling  in  exception- 
ally good  examples  to  o.oi,  British  units  being  used. 

M.  Havez  has  found  a  similar  expression  to  be  practically 
correct  for  heating-surfaces,  and  asserts  that  we  may  take  the 
quantity  of  heat  transmitted  in  either  case  as  decreasing  in 
geometrical  progression ;  while  the  length  of  path  swept  over, 
measured  from  the  origin,  increases  in  arithmetical  progres- 
sion.* Mr.  Williams  and  M.  Petiet  both  found,  in  experi- 
ments on  locomotives,  that  the  evaporation  diminished  about 
one  half  at  each  step,  metre  by  metre,  or  yard  by  yard,  from 
the  furnace  to  the  smoke-box  end  of  the  tubes. 

The  efficiency  of  the  heating-surfaces  of  boilers  has  been 
sometimes  considerably  increased  by  the  expedient  of  setting 
pins  in  the  plates  in  such  manner  that,  projecting  into  the  flue 
or  furnace  on  the  one  side  and  the  water-space  on  the  other, 
they  take  up  heat  from  the  passing  gases  and  conduct  it  into  the 
midst  of  the  water.  A  pin  may  be  thus  made  to  absorb  and 

*  Revue  Industrielk •,  Mch.,  1874. 


228  THE   STEAM-BOILER. 

utilize  several  times  as  much  heat  as  could  be  taken  up  by  the 
section  of  the  sheet  occupied  by  it.  Such  "  conductor-pins'* 
have  often  been  introduced  into  marine  and  other  boilers,  with 
very  evident  improvement  in  results.  Even  corrugating  a 
sheet  will  produce  marked  advantage  in  this  manner,  especially 
where  the  direction  of  the  currents  is  across  the  lines  of  corru- 
gation. 

99.  The  Effect  of  Incrustation,  and  of  deposits  of  various 
kinds,  is  to  enormously  reduce  the  conducting  power  of  heat- 
ing-surfaces ;  so  much  so,  that  the  power,  as  well  as  the  eco- 
nomic efficiency  of  a  boiler,  may  become  very  greatly  reduced 
below  that  for  which  it  is  rated,  and  the  supply  of  steam  fur- 
nished by  it  may  become  wholly  inadequate  to  the  require- 
ments of  the  case. 

It  is  estimated  that  a  sixteenth  of  an  inch  (0.16  cm.)  thick- 
ness of  hard  "  scale"  on  the  heating-surface  of  a  boiler  will 
cause  a  waste  of  nearly  one  eighth  its  efficiency,  and  the  waste 
increases  as  the  square  of  its  thickness.  The  boilers  of  steam- 
vessels  are  peculiarly  liable  to  injury  from  this  cause  where 
using  salt  water,  and  the  introduction  of  the  surface-condenser 
has  been  thus  brought  about  as  a  remedy.  Land  boilers  are 
subject  to  incrustation  by  the  carbonate  and  other  salts  of  lime, 
and  by  the  deposit  of  sand  or  mud  mechanically  suspended  in 
the  feed-water. 

It  has  been  estimated  that  the  annual  cost  of  operation  of 
locomotives  in  limestone  districts  is  increased  $750  by  deposits 
of  scale. 


CHAPTER  V. 

HEAT  AS   ENERGY — ENERGETICS   AND   THERMODYNAMICS. 

100.  Heat  as  a  Form  of  Energy  is  subject  to  the  general 
laws  which  govern  every  form  of  energy  and  control  all  matter 
in  motion,  whether  that  motion  be  molecular  or  the  movement 
of  masses.  Under  the  title  "  Energetics"  are  comprehended 
all  laws  affecting  bodies,  molecules,  or  atoms  in  relative  motion. 

That  heat  is  the  motion  of  the  molecules  of  bodies  was  first 
shown  by  experiment  by  Benjamin  Thompson,  Count  Rumford, 
then  in  the  service  of  the  Bavarian  Government,  who  in  1798 
presented  a  paper  to  the  Royal  Society  of  Great  Britain, 
describing  his  work,  and  reciting  the  results  and  his  conclusion 
that  heat  is  not  substance,  but  a  form  of  energy. 

This  paper  is  of  very  great  historical  interest,  as  the  now 
accepted  doctrine  of  the  persistence  of  energy  is  a  generaliza- 
tion which  arose  out  of  a  series  of  investigations,  the  most  im- 
portant of  which  are  those  which  resulted  in  the  determination 
of  the  existence  of  a  definite  quantivalent  relation  between 
these  two  forms  of  energy  and  a  measurement  of  its  value,  now 
known  as  the  "  mechanical  equivalent  of  heat."  The  experi- 
ment consisted  in  the  determination  of  the  quantity  of  heat 
produced  by  the  boring  of  a  cannon  at  the  arsenal  at  Munich. 

Rumford,  after  showing  that  this  heat  could  not  have  been 
derived  from  any  of  the  surrounding  objects,  or  by  compression 
of  the  materials  employed  or  acted  upon,  says :  "  It  appears  to 
me  extremely  difficult,  if  not  impossible,  to  form  any  distinct 
idea  of  anything  capable  of  being  excited  and  communicated  in 
the  manner  that  heat  was  excited  and  communicated  in  these 
experiments,  except  it  be  motion."  *  He  estimates  the  heat 

*This  idea  was  not  by  any  means  original  with  Rumford.  Bacon  seems  to 
have  had  the  same  idea;  and  Locke  says,  explicitly  enough:  "  Heat  is  a  very 
brisk  agitation  of  the  insensible  parts  of  the  object,  ...  so  that  what  in  our  sen- 
sation is  heat,  in  the  object  is  nothing  but  motion." 


230  THE   STEAM-BOILER. 

produced  by  a  power  which  he  states  could  easily  be  exerted 
by  one  horse,  and  makes  it  equal  to  the  "  combustion  of  nine 
wax  candles,  each  three  quarters  of  an  inch  in  diameter,"  and 
equivalent  to  the  elevation  of  "  25.68  pounds  of  ice-cold  water" 
to  the  boiling-point,  or  4784.4  heat-units.*  The  time  was 
stated  at  "  150  minutes."  Taking  the  actual  power  of  Rum- 
ford's  Bavarian  "  one  horse"  at  the  most  probable  figure,  25,000 
pounds  raised  one  foot  high  per  minute,  f  this  gives  the 
"  mechanical  equivalent  "  of  the  foot-pound  as  783.8  heat-units, 
differing  but  1.5  per  cent  from  the  now  accepted  value. 

Had  Rumford  been  able  to  measure  his  power  and  to 
eliminate  all  losses  of  heat  by  evaporation,  radiation,  and  con- 
duction, to  which  losses  he  refers,  and  to  measure  the  power 
exerted  with  accuracy,  the  result  would  have  been  exact. 
Rumford  thus  made  the  experimental  discovery  of  the  real 
nature  of  heat,  proving  it  to  be  a  form  of  energy,  and,  publish- 
ing the  fact  a.  half-century  before  the  now  standard  determina- 
tions were  made,  gave  us  a  very  close  approximation  to  the 
value  of  the  heat-equivalent.  He  also  observed  that  the  heat 
generated  was  "  exactly  proportional  to  the  force  with  which 
the  two  surfaces  are  pressed  together,  and  to  the  rapidity  of 
the  friction,"  which  is  a  simple  statement  of  equivalence  be- 
tween the  quantity  of  work  done,  or  energy  expended,  and  the 
quantity  of  heat  produced.  This  was  the  first  great  step  toward 
the  formation  of  a  Science  of  Thermodynamics. 

Sir  Humphry  Davy,  a  little  later  (1799),  published  the 
details  of  an  experiment  which  conclusively  confirmed  these 
deductions  from  Rumford's  work.  He  rubbed  two  pieces  of 
ice  together,  and  found  that  they  were  melted  by  the  friction 
so  produced.  He  thereupon  concluded  :  "  It  is  evident  that 
ice  by  friction  is  converted  into  water.  .  .  .  Friction,  conse- 
quently, does  not  diminish  the  capacity  of  bodies  for  heat." 

*  The  British  heat-unit  is  the  quantity  of  heat  required  to  heat  one  pound  of 
water  i°  Fahr.  from  the  temperature  of  maximum  density. 

f  Rankine  gives  25,920  foot-pounds  per  minute — or  432  per  second — for  the 
average  draught-horse  in  Great  Britain,  which  is  probably  too  high  for  Bavaria. 
The  engineer's  "  horse-power" — 33,000  foot-pounds  per  minute — is  far  in  excess 
of  the  average  power  of  even  a  good  draught -horse,  which  latter  is  sometimes 
taken  as  two  thirds  the  former. 


HEAT  AS  ENERGY.  231 

Bacon  and  Newton,  and  Hook  and  Boyle,  seem  to  have  an- 
ticipated— long  before  Rumford's  time — all  later  philosophers, 
in  admitting  the  probable  correctness  of  that  modern  dynami- 
cal, or  vibratory,  theory  of  heat  which  considers  it  a  mode  of 
motion;  but  Davy,  in  1812,  for  the  first  time,  stated  plainly 
and  precisely  the  real  nature  of  heat,  saying:  "  The  immediate 
cause  of  the  phenomenon  of  heat,  then,  is  motion,  and  the  laws 
of  its  communication  are  precisely  the  same  as  the  laws  of  the 
communication  of  motion."  The  basis  of  this  opinion  was  the 
same  that  had  previously  been  noted  by  Rumford. 

So  much  having  been  determined,  it  became  at  once  evident 
that  the  determination  of  the  exact  value  of  the  mechanical 
equivalent  of  heat  was  simply  a  matter  of  experiment ;  and 
during  the  succeeding  generation  this  determination  was  made, 
with  greater  or  less  exactness,  by  several  distinguished  men. 
It  was  also  equally  evident  that  the  laws  governing  the  new 
science  of  thermodynamics  could  be  mathematically  ex- 
pressed. 

Fourier  had,  before  the  date  last  given,  applied  mathemati- 
cal analysis  in  the  solution  of  problems  relating  to  the  transfer 
of  heat  without  transformation,  and  his  "  Theorie  de  la  Cha- 
leur"  contained  an  exceedingly  beautiful  treatment  of  the  sub- 
ject. Sadi  Carnot,  twelve  years  later  (1824),  published  his 
"  Reflexions  sur  la  Puissance  Motrice  du  Feu,"  in  which  he 
made  a  first  attempt  to  express  the  principles  involved  in  the 
application  of  heat  to  the  production  of  mechanical  effect. 
Starting  with  the  axiom  that  a  body  which,  having  passed 
through  a  series  of  conditions  modifying  its  temperature,  is 
returned  to  "  its  primitive  physical  state  as  to  density,  tem- 
perature, and  molecular  constitution,"  must  contain  the  same 
quantity  of  heat  which  it  had  contained  originally,  he  shows 
that  the  efficiency  of  heat-engines  is  to  be  determined  by  carry- 
ing the  working  fluid  through  a  complete  cycle,  beginning  and 
ending  with  the  same  set  of  conditions.  Carnot  was  not  a 
believer  in  the  vibratory  theory  of  heat,*  and  consequently  was 
led  into  some  errors ;  but,  as  will  be  seen  hereafter,  the  idea 

*  Documents  recently  discovered  (Comptes  Rendus,  1878,  p.  967)  either  show 
this  to  be  an  error  or  prove  his  later  conversion. 


232  THE   STEAM-BOILER. 

just  expressed  is  one  of  the  most  important  details  of  a  theory 
of  the  steam-engine. 

Seguin,  who  has  already  been  mentioned  as  one  of  the  first 
to  use  the  fire-tubular  boiler  for  locomotive  engines,  published 
in  1839  a  work,  "  Sur  1'Influence  des  Chemins  de  Fer,"  in  which 
he  gave  the  requisite  data  for  a  rough  determination  of  the 
value  of  the  mechanical  equivalent  of  heat,  although  he  does 
not  himself  deduce  that  value. 

Dr.  Mayer  of  Heilbronn,  three  year's  later  (1842),  published 
the  results  of  a  very  ingenious  and  quite  closely  approximate 
calculation  of  the  heat-equivalent,  basing  his  estimate  upon  the 
work  necessary  to  compress  air,  and  on  the  specific  heats  of  the 
gas,  the  idea  being  that  the  work  of  compression  is  the  equiva- 
lent of  the  heat  generated.  Seguin  had  taken  the  converse 
operation,  taking  the  loss  of  heat  of  expanding  steam  as  the 
equivalent  of  the  work  done  by  the  steam  while  expanding. 
The  latter  also  was  the  first  to  point  out  the  fact,  afterward 
experimentally  proved  by  Hirn,  that  the  fluid  exhausted  from 
an  engine  should  heat  the  water  of  condensation  less  than 
would  the  same  fluid  when  originally  taken  into  the  engine. 

A  Danish  engineer,  Colding,  at  about  the  same  time  (1843), 
published  the  results  of  experiments  made  to  determine  the 
same  quantity ;  but  the  best  and  most  extended  work,  and 
that  which  is  now  almost  universally  accepted  as  standard,  was 
done  by  a  British  investigator. 

Joule  commenced  the  experimental  investigations,  seeking 
a  measure  of  the  relations  of  heat  and  work,  which  have  made 
him  famous,  at  some  time  previous  to  1843,  at  which  date  he 
published,  in  the  Philosophical  Magazine,  his  earliest  method. 
His  first  determination  gave  770  foot-pounds.  During  the 
succeeding  five  or  six  years  Joule  repeated  his  work,  adopting 
a  considerable  variety  of  methods,  and  obtaining  very  variable 
results.  One  method  was  to  determine  the  heat  produced  by 
forcing  air  through  tubes ;  another,  and  his  usual  plan,  was  to 
turn  a  paddle-wheel  by  a  definite  power  in  a  known  weight  of 
water.  He,  in  1849,  concluded  these  researches,  and  announced 
finally  the  value  772  foot-pounds  as  that  of  the  mechanical 
equivalent  of  the  British  heat-unit. 


HEAT  AS  ENERGY.  233 

101.  Energetics  treats  of  modifications  of  energy  under 
the  action  of  forces,  and  of  its  transformation  from  one  mode 
of  manifestation  to  another,  and  from  one  body  to  another, 
and  within  this  broader  science  is  comprehended  that  latest  of 
the  minor  sciences,  of  which  the  heat-engines  and  especially 
the  steam-engine  illustrate  the  most  important  applications — 
Thermodynamics.  The  science  of  energetics  is  simply  a  wider 
generalization  of  principles  which  have  been  established  one  at 
a  time,  and  by  philosophers  widely  separated  both  geographi- 
cally and  historically,  by  both  space  and  time,  and  which  have 
been  slowly  aggregated  to  form  one  after  another  of  the  physi- 
cal sciences,  and  out  of  which,  as  we  now  are  beginning  to  see, 
we  are  slowly  evolving  wider  generalizations,  and  thus  tending 
toward  a  condition  of  scientific  knowledge  which  renders  more 
and  more  probable  the  truth  of  Cicero's  declaration :  "  One 
eternal  and  immutable  law  embraces  all  things  and  all  times." 
At  the  basis  of  the  whole  science  of  energetics  lies  a  principle 
which  was  enunciated  before  Science  had  a  birthplace  or  a 
name : 

All  that  exists,  'whether  matter  or  force,  and  in  whatever 
.  form,  is  indestructible,  except  by  the  Infinite  Power  which  has 
created  it. 

That  matter  is  indestructible  by  finite  power  became  ad- 
mitted as  soon  as  the  chemists,  led  by  their  great  teacher  La- 
voisier, began  to  apply  the  balance,  and  were  thus  able  to  show 
that  in  all  chemical  change  there  occurs  only  a  modification  of 
form  or  of  combination  of  elements,  and  no  loss  of  matter  ever 
takes  place.  The  "  persistence"  of  energy  was  a  later  dis- 
covery, consequent  largely  upon  the  experimental  determina- 
tion of  the  convertibility  of  heat-energy  into  other  forms  and 
into  mechanical  work,  for  which  we  are  indebted  to  Rumford 
and  Davy,  and  to  the  determination  of  the  quantivalence 
anticipated  by  Newton,  shown  and  calculated  approximately 
by  Colding  and  Mayer,  and  measured  with  great  probable 
accuracy  by  Joule. 

It  is  now  generally  understood  that  all  forms  of  energy  are 
mutually  convertible  with  a  definite  quantivalence ;  and  it  is 
not  certain  that  even  vital  and  mental  energy  do  not  fall  within 


234  THE   STEAM-BOILER. 

the  same  great  generalization.  This  quantivalence  is  the  basis 
of  the  science  of  energetics. 

Experimental  investigation  and  analytical  research  have 
together  thus  created  a  new  science,  and  the  philosophy  of  the 
steam-engine  has  at  last  been  given  a  complete  and  well-defined 
form,  enabling  the  intelligent  engineer  to  comprehend  the  opera- 
tion of  the  machine,  to  perceive  the  conditions  of  efficiency, 
and  to  look  forward  in  a  well-settled  direction  for  further  ad- 
vances in  its  improvement  and  in  the  increase  of  its  efficiency. 

Energy  is  the  capacity  of  a  moving  body  to  overcome  resist- 
ance offered  to  its  motion  ;*  it  is  measured  either  by  the  prod- 
uct of  the  mean  resistance  into  the  space  through  which  it  is 
overcome,  or  by  the  half  product  of  the  mass  of  a  free  body  into 
the  square  of  its  velocity.  Kinetic  energy  is  the  actual  energy 
of  a  moving  body ;  potential  energy  is  the  measure  of  the  work 
which  a  body  is  capable  of  doing  under  certain  conditions 
which,  without  expending  energy,  may  be  made  to  affect  it,  as 
by  the  breaking  of  a  cord  by  which  a  weight  is  suspended,  or 
by  firing  a  mass  of  explosive  material.  The  British  measure 
of  energy  is  the  foot-pound  ;  the  metric  measure  is  the  kilo- 
grammetre. 

Energy,  whether  kinetic  or  potential,  may  be  observable 
and  due  to  mass-motion  ;  or  it  may  be  invisible  and  due  to 
molecular  movements.  The  energy  of  a  heavenly  body  or  of 
a  coiled  spring,  and  that  of  heat  or  of  electrical  action,  are  illus- 
trations of  the  two  classes.  In  Nature  we  find  utilizable  poten- 
tial energy  in  fuel,  in  food,  in  any  available  head  of  water,  and 
in  available  chemical  affinities.  We  find  kinetic  energy  in  the 
motion  of  the  winds  and  the  flow  of  running  water,  in  the  heat- 
motion  of  the  sun's  rays,  in  heat-currents  on  the  earth,  and  in 
many  intermittent  movements  of  bodies  acted  on  by  applied 
forces,  natural  or  artificial.  The  potential  energy  of  fuel  and 
of  food  has  already  been  seen  to  have  been  derived,  at  an 
earlier  period,  from  the  kinetic  energy  of  the  sun's  rays,  the 
fuel  or  the  food  being  thus  made  a  storehouse  or  reservoir  of 


*  The  term  "  energy"  was  first  used  by  Dr.  Young  as  the  equivalent  of  the 
work  of  a  moving  body,  in  his  "  Lectures  on  Natural  Philosophy"  (1807). 


HEAT  AS  ENERGY.  235 

energy.  It  is  also  seen  that  the  animal  system  is  simply  a 
"mechanism  of  transmission"  for  energy,  and  does  not  create 
but  simply  diverts  it  to  any  desired  direction  of  application. 

All  the  available  forms  of  energy  can  be  readily  traced  back 
to  a  common  origin  in  the  potential  energy  of  a  universe  of 
nebulous  substance  (chaos),  consisting  of  infinitely  diffused 
matter  of  immeasurably  slight  density,  whose  "  energy  of  posi- 
tion" had  been,  since  the  creation,  gradually  going  through  a 
process  of  transformation  into  the  several  forms  of  kinetic  and 
potential  energy  above  specified,  through  intermediate  methods 
of  action  which  are  usually  still  in  operation,  such  as  the  poten- 
tial energy  of  chemical  affinity,  and  the  kinetic  forms  of  energy 
seen  in  solar  radiation,  the  rotation  of  the  earth,  and  the  heat 
of  its  interior. 

The  measure  of  any  given  quantity  of  energy,  whatever  may 
be  its  form,  is  the  product  of  the  resistance  which  it  is  capable 
of  overcoming  into  the  space  through  which  it  can  move 
against  that  resistance,  i.e.,  by  the  product  RS,  or  the  equiva- 

WV* 
lent  expressions and  ^MV*,  in  which  W  is  the  weight,  M 

o 

the  "mass"  of  matter  affected  by  the  motion,  Fthe  velocity, 
and  g  the  dynamic  measure  of  gravity. 
The  three  great  taws  of  energetics  are  : 

(1)  The  sum  total  of  the  energy,  active  and  potential,  of  the 
universe  is  invariable. 

(2)  The  several  forms  of  energy  are  all  interconvertible,  and 
possess  a  definite  quantivalence. 

(3)  All  forms  of  kinetic  energy  are  tending  toward  reduc- 
tion to  forms  of  molecular  motion  and  final  dissipation  through- 
out space. 

102.  Heat-energy  and  Temperature  are  closely  related 
and  directly  proportional,  the  one  to  the  other. 

The  investigations  of  physicists  have  shown  that  when  p 
and  v  are  the  pressure  and  volume  of  unit  weight  of  any  gas, 
and  c  is  the  velocity  of  molecules  having  the  mass  m  and  in 
number  n, 

pv  =  \rnnc* ; (i) 


236  THE   STEAM-BOILER. 

it  is  also  known  that 

......        ,.    (2) 


when  ^?  =  -^,  the  subscripts  denoting  that  these  quantities 

^o 

are  taken  at  the  freezing-point  of  water,  and  T  is  the  tempera- 
ture measured  from  the  absolute  zero,  as  hereafter  defined 
(—  46i°.2  F.,  or  —  274°  C.)|  hence 


(3) 


and  the  temperature  of  any  substance,  measured  on  the  abso- 
lute scale,  is  proportional  to  the  kinetic  energy  of  the  molecules 
constituting  the  gas.  In  other  words,  as  elsewhere  stated, 
temperature  is  a  measure  of  the  intensity  of  molecular  vibra- 
tion, while  quantity  of  heat,  as  has  been  seen,  is  quantity  of 
molecular  energy  of  vibration. 

Thus  temperature,  as  measured  on  the  absolute  scale  and 
on  the  air-thermometer,  is  directly  proportional  to  the  molec- 
ular energy  of  any  given  mass,  and  thus,  in  the  case  of  any 
confined  gas,  measures  the  intensity  of  pressure  on  the  enclos- 
ing walls  due  to  the  heat-energy  so  imprisoned,  which  quan- 
tity is  also  proportional  to  the  product  of  this  pressure  into  the 
volume  of  the  space  throughout  which  it  is  exerted. 

103.  Quantitative  Measures  of  Heat-energy,  obtained  by 
the  various  systems  of  calorimetry,  always  involve  determina- 
tions of  the  magnitudes  of  factors  the  product  of  which  give 
the  quantity  of  molecular  energy  present.  These  factors  have 
been  seen  to  be  either  measures  of  the  mass  affected  and  of 
molecular  velocity,  or  thermal  equivalents.  The  quantity  of 
heat-energy  to  be  measured  is  obtained  either  by  multiplying  the 
mass  by  the  square  of  velocity  of  vibration,  or  by  the  product 
of  the  weight  into  the  range  of  temperature  considered  and  the 
mean  specific  heat  :  these  two  measures  are  equivalent.  It 
is  by  either  method  made  evident  that  temperature  is  one 
factor  of  a  product  which  is  the  measure  of  heat-energy,  the 


HEAT  AS  ENERGY.  237 

other  factor  being  a  measure  of  the  mass  of  matter  acting  as 
the  vehicle  of  that  energy. 

104.  Heat  Transformations  may  take  place,  through  the 
action  of  physical  and  chemical   forces,  into  any  other  known 
form  of  energy,  and  another  form  of  energy  may  be  transmuted 
into    heat.       Nearly  all  physical   phenomena,  in  fact,  involve 
heat-transformation  in  one  form  or  another,  and  in  a  greater  or 
a  less  degree,  under  the  laws  of  energetics.     According  to  the 
first  of  those  laws,  such  changes  must  always  occur  by  a  defi- 
nite quantivalence,  and  when  heat  disappears  in  known  quan- 
tity it  is  always  certain  that  energy  of  calculable  amount  will 
appear  as  its  equivalent ;  the  reverse  is  as  invariably  the  case 
when  heat  is  produced ;  it  always  represents  and  measures  an 
equivalent  amount  of  mechanical,  electrical,  chemical,  or  other 
energy. 

105.  Heat   and  Mechanical   Energy   are   thus   evidently 
subject  to  the  general  laws  of  transformation  of  energy,  and  the 
transmutation  of  the  one  into  the  other. must  always  be  capa- 
ble of  treatment  mathematically.     The  relations  of  these  two 
forms  of  energy  are  thought  by  the  physicist  and  the  engineer 
as  of  sufficient  importance,  and  the  phenomena  involving  these 
relations  alone  are  so  often  found  to  demand  and  to  permit  in- 
dependent consideration,  that  they  are  taken  as  the  subject  of 
a  division  of  energetics  known  as  the  science  of  thermodynamics, 
and  a  vast  amount  of  study  and  research  has  been  given  by  the 
ablest  mathematical  physicists  of  modern  times  to  the  investi- 
gation of  its  laws  and  their  applications,  and  to  the  building  up 
of  that  science. 

The  conversion  of  water  into  steam  in  the  steam-boiler  and 
the  utilization  of  the  heat-energy  thus  made  available,  or  in 
heated  air  and  other  gases,  in  steam-  or  other  heat-engines,  con- 
stitute at  once  the  most  familiar  and  the  most  important  of 
known  illustrations  of  thermodynamic  phenomena  and  their 
useful  application.  The  process  of  making  steam  is  one  of  pro- 
duction of  heat  by  transformation  from  the  potential  form  of 
energy  through  the  action  of  chemical  forces,  and  its  storage 
in  sensible  form  for  later  use  in  the  steam-engine,  where  it  is 
changed  into  equivalent  mechanical  energy.  The  pure  science 


238  THE   STEAM-BOILER. 

of  the  steam-engine  is  thus  the  science  of  thermodynamics, 
the  first  applications  of  which  are  made  in  the  operations 
carried  on  in  the  steam-boiler. 

106.  Thermodynamics  is  that  science  which  treats  solely 
of  the  relations  of  heat  and  the  mechanical  form  of  energy,  of 

o^  " 

the  establishment  of  the  laws  governing  their  interconversion, 
and  of  the  applications  of  those  laws. 

The  science  of  thermodynamics  is,  as  has  been  stated,  a 
branch  of  the  science  of  energetics,  and  is  the  only  branch  of 
that  science  in  the  domain  of  the  physicist  which  has  been  very 
much  studied.  This  branch  of  science,  which  is  restricted  to 
the  consideration  of  the  relations  of  heat-energy  to  mechanical 
energy,  is  based  upon  the  great  fact  determined  by  Rumford 
and  Joule,  and  considers  the  behavior  of  those  fluids  which 
are  used  in  heat-engines  as  the  media  through  which  energy  is 
transferred  from  the  one  form  to  the  other.  As  now  accepted, 
it  assumes  the  correctness  of  the  hypothesis  of  the  dynamic 
theory  of  fluids,  which  supposes  their  expansive  force  to  be  due 
to  the  motion  of  their  molecules. 

This  idea  is  as  old  as  Lucretius,  and  was  distinctly  ex- 
pressed by  Bernouilli,  Le  Sage  and  Prevost,  and  Herapath. 
Joule  recalled  attention  to  this  idea  in  1848,  as  explaining  the 
pressure  of  gases  by  the  impact  of  their  molecules  upon-  the 
sides  of  the  containing  vessels.  Helmholtz,  ten  years  later, 
beautifully  developed  the  mathematics  of  media  composed  of 
moving,  frictionless  particles  ;  and  Clausius  has  carried  on  the 
work  still  further. 

The  general  conception  of  a  gas,  as  held  to-day,  including 
the  vortex-atom  theory  of  Thomson  and  Rankine,  supposes  all 
bodies  to  consist  of  small  particles  called  molecules,  each  of 
which  is  a  chemical  aggregation  of  its  ultimate  parts  or  atoms. 
These  molecules  are  in  a  state  of  continual  agitation,  which  is 
known  as  heat-motion.  The  higher  the  temperature,  the  more 
violent  this  agitation ;  the  total  quantity  of  motion  is  measured 
as  vis  viva  by  the  half-product  of  the  mass  into  the  square  of 
the  velocity  of  molecular  movement,  or  in  heat-units  by  the 
same  product  divided  by  Joule's  equivalent.  In  solids,  the 
range  of  motion  is  circumscribed,  and  change  of  form  cannot 


HEAT  AS  ENERGY.  239 

take  place.  In  fluids,  the  motion  of  the  molecules  has  become 
sufficiently  violent  to  enable  them  to  break  out  of  this  range, 
and  their  motion  is  then  no  longer  definitely  restricted.  The 
science  of  thermodynamics  finds  application  in  every  phenome- 
non in  which  these  various  manifestations  of  heat-energy  are 
accompanied  by  the  performance  of  work  or  result  from  such 
work. 

107.  The  First  Law  of  Thermodynamics  is  a  simple 
corollary  of  the  first  law  of  energetics ;  it  is  enunciated  as  fol- 
lows : 

Heat-energy  and  mechanical  energy  are  mutually  convertible 
and  have  a  definite  equivalence. 

The  British  thermal  unit  being  equivalent  to  772  foot- 
pounds of  work,  nearly,  and  the  metric  calorie  to  423.55,  or,  as 
usually  taken,  424  kilogrammetres.* 

The  first  precise  and  direct  determinations  of  the  mechani- 
cal equivalent  of  the  thermal  unit  were  made  by  Joule,  by  sev- 
eral methods.  He  stated  the  results  of  his  researches  relating 
to  the  mechanical  equivalent  of  heat  as  follows : 

(1)  The  heat  produced  by  the  friction  of  bodies,  whether 
solid  or  liquid,  is  always  proportional  to  the  quantity  of  work 
expended. 

(2)  The  quantity  required  to  increase  the  temperature  of 
a  pound  of  water  (weighed  in  vacuo  at  55°  to  60°  Fahr.)  by  one 
degree  requires  for  its  production  the  expenditure  of  a  force 
measured  by  the  fall  of  772  pounds  from  a  height  of  one  foot. 
This  quantity  is  now  generally  called  "  Joule's  equivalent." 

During  this  series  of  experiments  Joule  also  deduced  the 
position  of  the  "  absolute  zero,"  the  point  at  which  heat-motion 
ceases,  and  stated  it  to  be  about  480°  Fahr.  below  the  freezing- 
point  of  water,  which  is  not  very  far  from  the  probably  true 
value,  —  493°. 2  Fahr.  (—  273°  C.),  as  deduced  afterward  from 
more  precise  data. 

This  first  law  is  that  by  the  application  of  which  we  deduce 
a  measure  of  the  quantity  of  work  done  whenever  a  known 

*  A  committee  of  the  British  Association  reported  its  value  (1878)10  be  772.58 
foot-pounds,  and  a  later  figure  is  774,  with  a  limit  of  error  of  about  two  per  cent. 


240  THE   STEAM-BOILER. 

amount  of  heat  is  transformed  ;  it  does  not  determine  how  much 
in  any  case  will  be  transformed.  For  example,  for  any  heat- 
engine  we  may  calculate  precisely  how  much  is  demanded  for  the 
performance  of  work  when  it  is  known  how  much  work  is  done  ; 
but  this  law  affords  no  means  of  determining,  in  any  such  case, 
what  proportion  of  the  heat-energy  sent  into  the  system  will 
be  converted  into  work,  or  what  part  will  pass  through  untrans- 
formed  ;  and  it  hence  gives  no  clue  to  the  total  quantity  of 
heat  called  for,  or  of  steam  to  be  made  at  the  boiler,  even 
though  all  wastes  by  conduction  and  radiation  be  discovered 
and  measured.  This  clue  is  given  by  the  second  law,  which 
will  also  enable  us  to  determine  the  amount  of  thermodynam- 
ically  unavoidable  loss. 

108.  The  Second  Law  of  Thermodynamics  is  stated  in 
a  great  variety  of  ways  by  various  writers,  and  is  not  always 
clearly  enunciated  by  the  best  authorities.  The  following 
method  of  statement  is  adapted  especially  to  present  purposes  : 

In  the  transfer  or  the  transformation  of  heat-energy,  the  total 
effect  produced  is  directly  proportional  to  the  total  quantity  of 
heat  present  and  acting. 

Thus,  if  the  effect  of  heat  be  to  produce  change  of  pressure, 
change  of  volume,  or  variation  of  temperature,  the  magnitude 
of  that  alteration  of  pressure,  of  temperature,  or  of  volume  will 
be  directly  proportional  to  the  quantity  of  heat  concerned  in 
its  production.  This  law  is  based  upon  the  almost  axiomatic 
proposition,  that  heat-energy  is  homogeneous,  and  equal  quan- 
tities must  invariably  be  capable  of  causing  equal  effects. 

Since,  in  any  mass  of  matter  acting  as  a  reservoir  or  vehicle 
of  heat-energy,  the  quantity  of  heat  present  is  proportional  to 
its  absolute  temperature,  it  follows,  from  what  has  preceded, 
that  the  effect  produced  by  any  thermal  variation  in  a  heated 
mass  is  proportional  to  the  absolute  temperature  at  which  the 
action  takes  place.  These  propositions  and  the  second  law  of 
thermodynamics  are  expressed  algebraically  by  the  equations 


d_        d_     Q  _.  ,, 

d~     dT     T~'  • 


HEAT  AS  ENERGY.  24! 

in  which  Q  and  T  are  the  quantity  of  heat  contained  in  the 
body  and  its  absolute  temperature.  In  other  words,  the  prod- 
uct of  the  absolute  temperature  by  the  ratio  of  variation  of 
any  quantity  with  temperature  is  equal  to  the  product  of  the 
heat  acting  into  the  rate  of  variation  of  that  quantity  with  the 
variation  of  heat. 

The  quantity  of  work  performed  by  transformation  of  heat 
is  measured  by 


=QlU  =  TdU\  .     .     .     .     ,     (2) 


which  will  become  known  when  the  law  of  variation  of  work, 
dUj  with  heat,  Q,  can  be  given. 

109.  The  Molecular  Constitution  of  Matter  and  its  physical 
structure  and  state  determine  precisely  how  heat  will  affect  it, 
and  just  how  it  will  behave  in  the  storage,  transfer,  and  transfor- 
mation of  that  energy  into  other  forms.  All  matter  consists  of 
particles  or  molecules,  sometimes  simple,  but  usually  complex, 
affected  by  the  forces  which  become  observable  under  the  action 
of  one  body  upon  another.  These  forces  are  either  attractive, 
repulsive,  or  directive.  Thus,  heat  produces  a  mutual  repul- 
sion of  molecules,  and,  if  permitted  by  surrounding  masses,  the 
body  expands  with  its  reception.  Cohesion  is  an  attractive 
force,  as  is  gravitation,  while  magnetic  and  electric  forces  may 
be  either  attractive  or  repellent  ;  and  the  polarity  seen  in  the 
formation  of  crystals  and  magnetism  gives  directive  power  —  the 
first  determining  the  method  of  aggregation  of  approximating 
molecules,  the  last  the  positions  assumed  by  the  molecules 
affected  by  it.  The  property  of  inertia  is  common  to  all  forms 
of  matter,  and  is  essential  to  the  production  of  all  the  phe- 
nomena observed  in  the  motion  and  mutual  actions  of  free 
bodies. 

1  10.  Solids  are  bodies  in  which  the  attractive  and  directive 
forces  are  sufficiently  powerful  to  give  stability  both  of  form 
and  of  volume.  Liquids  have  stability  of  volume  but  not  of 
form  ;  while  gases  and  vapors  have  stability  neither  of  form  nor  of 
volume,  and  in  them  the  repellent  forces  have  more  intensity 
16 


242  THE   STEAM-BOILER. 

than  the  attractive.  In  gases  the  latter  become  insensible,  and 
in  the  hypothetical  "  perfect  "  gas  cease  to  exist.  All  interme- 
diate degrees  of  stability  exist  among  the  substances  known  in 
nature,  and  no  known  form  of  matter  can  be  assigned  to  either 
class  as  a  perfect  representative  of  the  combination  of  properties 
defining  it.  In  passing  from  one  state  to  another,  substances 
traverse  these  intermediate  conditions.  Ice,  water,  and  steam 
illustrate  the  three  -typical  classes  of  matter.  In  the  first  the 
attractive  and  directive  forces  give  stability  of  form  and  strength  ; 
in  the  second,  no  stability  of  form  exists,  but  some  tenacity  or 
cohesive  power  remains,  which  cannot  be  easily  detected  in  con- 
sequence of  the  freedom  of  relative  motion  permitted  among 
its  particles  when  polarity  disappears  ;  in  the  third  form  of  the 
same  substance  the  fluid  must  be  confined  within  walls  capable 
of  sustaining  its  outward  pressure  to  keep  it  from  indefinite  ex- 
pansion. 

The  thermodynamic  definition  of  a  perfect  gas  is  found  in 
the  equation 

pv      p.v. 

£—  —  *-7=r  =  R,  a  constant, 
*          *  i 

the  product  of  pressure  and  volume  always  varying  with  the 
absolute  temperature. 

ill.  Heat  and  Matter  have  this  peculiar  relation,  that 
while  all  other  forces  which  commonly,  with  that  due  to  the 
presence  of  heat,  determine  to  which  of  the  three  physical  states 
the  latter  shall  be  assigned,  are  definitely  related  to  the  sub- 
stance, having  magnitudes  which  are  functions  of  volume  and 
of  molecular  distances,  the  force  introduced  with  heat,  and 
which  is  always  repellent,  is  variable,  independently  of  all  other 
conditions,  and  is,  in  fact,  constantly  so  varying. 

It  is  the  introduction  or  the  removal  of  heat  energy  from  mat- 
ter which  produces  all  familiar  physical  changes  of  states.  When 
a  solid  is  heated  it  is  expanded  against  the  resisting  efforts  of  all 
other  internal  and  external  forces,  and  after  a  time  the  quan- 
tity of  heat  and  the  temperature  attaining  a  limit  which  is  per- 
fectly definite  for  each  substance,  the  directive  force  becomes 


HEAT  AS  ENERGY.  243 

insensible,  and  the  mass  becomes  liquid.  The  introduction  of 
heat  continuing,  the  separation  of  molecules  continues  until  the 
cohesive  force  becomes  insensible,  or  at  least  less  than  the  ex- 
pansive force  of  the  heat,  and  the  fluid  is  converted  into  a 
vapor  ;  and  finally,  when  the  attractive  forces  disappear  en- 
tirely, into  gas.  In  this  process,  internal  forces  being  overcome, 
internal  work  is  performed,  and  external  forces  being  overcome, 
external  work  is  done  ;  while  a  certain  amount  of  heat,  not  so 
expended,  is  added  to  the  mass  as  sensible  heat,  and  thus  raises 
its  temperature. 

Specific  Heats  measure  the  quantity  of  heat  absorbed  by  unit 
weight  of  any  substance  in  a  change  of  temperature  of  one 
degree,  the  heat  being  either  all  or  partly  unchanged.  It  has 
been  already  defined  and  values  given  in  §  91.  Thermodynam- 
ically  considered,  it  is  seen  specific  heats  may  measure  either 
heat  or  work,  or  both. 

112.  Sensible  and  Latent  Heats  must  be  carefully  distin, 
guished  in  studying  the  action  of  heat  on  matter.     The  term 
"  sensible  heat  "  scarcely  requires  definition  ;  but  it  may  be  said 
that  sensible  and  latent    heats   represent    latent  and  sensible 
work ;  that  the  former  is  actual,  kinetic,  heat-energy,  capable  of 
transformation  into  mechanical   energy,  or  vis  viva  of  masses, 
and  into  mechanical  work;  while   the   latter  form  is  not  heat, 
but  is  the  equivalent  of  heat  transformed  to  produce  a  visible 
effect   in  the   performance  of  molecular,  or  internal  as  well  as 
external,  work,  and  visible  alteration  of  volume  and  other  phys- 
ical conditions. 

It  is  seen  that  heat  may  become  "  latent"  through  any 
transformation  which  results  in  a  definite  and  defined  physical 
change,  produced  by  expansion  of  any  substance  in  consequence 
of  such  transmutation  into  internal  and  external  work ;  whether 
it  be  simple  increase  of  volume  or  such  increase  with  change 
of  physical  state. 

113.  The  Latent  Heat  of  Expansion  is  a  name  for  that 
heat  which   is  demanded  to  produce  an  increase  of  volume,  as 
distinguished  from  that  untransformed  heat  which  is  absorbed 
by  the  substance  to  produce  elevation  of  temperature.     The 
latent  heat  of  expansion  may,  by  its  absorption  and  transforma- 


244  THE    STEAM-BOILER. 

tion,  and  the  resulting  performance  of  internal  and  external 
work,  cause  no  other  effect  than  change  of  volume,  as,  e.g., 
when  air  is  heated ;  or  it  may  at  the  same  time  produce  an 
alteration  of  the  solid  to  the  fluid,  or  of  the  liquid  to  the 
vaporous  state,  as  in  the  melting  of  ice  or  the  boiling  of  water, 
in  which  latter  cases,  as  it  happens,  no  elevation  of  temperature 
occurs,  all  heat  received  being  at  once  transformed.  In  the 
expansion  of  air,  and  in  other  cases  in  which  no  such  change 
of  state  occurs,  a  part  of  the  heat  absorbed  remains  unchanged, 
producing  elevation  of  temperature ;  while  another  part  is 
transformed  into  latent  heat  of  expansion. 

The  specific  heat  of  constant  volume,  no  molecular  or  other 
work  being  done,  measures  the  heat  untransformed,  and,  as 
sensible  heat,  producing  rrse  in  temperature.  The  specific  heat 
of  constant  pressure  measures  the  sum  of  the  sensible  and  latent 
heats,  when  a  gas  is  heated,  and  no  alteration  of  physical  state 
can  occur.  It  usually  is  assumed  to  include  both  internal  and 
external  work,  as  well  as  sensible  heat,  but  where  used  in  an 
unaccustomed  sense  the  conditions  of  the  case  are  always 
stated. 

114.  The  Latent  Heats  of  Fusion  and  of  Vaporization 
measure  the  quantities  of  heat  transformed  in  these  changes  of 
physical  state.     In  the  first  of  these  two  cases  the  work  done 
is  mainly  internal ;  in  the  second  the  internal  work  performed 
is  much   greater,  but   is   not  so   enormously  in  excess  of  the 
amount   of  external  work  done ;  and  the  higher  the  pressure 
under  which  vaporization  takes  place,  the  larger  proportionally 
the  measure  of  external  work  and  of  the  heat  demanded  for  its 
performance.     In   the  case  of  steam,  as  will  be  seen  later,  at 
ordinary  pressures,  the  ratio  of  internal  to   external  work  in 
this  change  of  state  is  about  as  ten  to   one.     All  this  work  is 
performed  in  the  expansion  of  the  mass  against  resisting  molec- 
ular attractive  forces,  unperceivable  and  incapable  of  measure- 
ment by  any  ordinary  pressure-gauge  or  physical  instrument. 

115.  The  Distribution  of  Heat  Energy  in  thermodynamic 
operations,  and  in  physical  changes  produced   by  it,  must  be 
carefully  studied,  and  must  be  represented  in  every  algebraic 
expression  in  the  mathematical  theory  of  the  subject.     As  has 


HEAT  AS  ENERGY.  245 

been  fully  shown,  the  absorption  of  heat  by  any  substance  often 
involves,  and  may  in  any  given  case  involve,  three  different 
applications ;  it  may  be  appropriated  to  the  elevation  of  tem- 
perature ;  to  the  expansion  of  the  mass  against  internal  forces, 
doing  internal  work ;  or  to  the  increase  of  its  volume,  overcom- 
ing external  pressures  and  performing  external  work.  On  the 
other  hand,  if  heat  is  received  from  any  substance,  it  may  be 
sensible  heat  simply  transferred  without  change ;  or  it  may  be 
heat  produced  by  transformation  out  of  work  through  the  action 
of  cohesive  forces ;  or  it  may  be  heat  similarly  resulting  from 
the  work  done  by  external  pressure  on  the  mass  during  its  com- 
pression. 

Whatever  the  manner  in  which  heat-energy  is  transferred 
or  transformed,  such  phenomena  as  are  observed  during  the  pro- 
cess are  subject  to  the  principles  which  have  been  stated,  and  the 
theory  of  the  process  is  constructed  by  the  application  of  the 
two  laws  which  have  been  enunciated,  and  in  that  manner  only. 
Every  algebraic  expression  representing  such  a  process  will  be 
a  statement  of  equality  between  the  total  amount  of  heat- 
energy  entering  or  leaving  the  substance,  and  the  sum  of  the 
variations  of  sensible  and  latent  heats  in  the  mass  affected. 

116.  The  Application  of  the  First  Law  leads  at  once  to 
the  construction  of  the  fundamental  equations  of  thermody- 
namics, and  permits  the  determination  of  their  constants.  The 
first  equation  to  be  established  is  simply  a  statement,  in  alge- 
braic language,  of  the  fact  that  the  total  quantity  of  heat  ab- 
sorbed or  rejected  by  any  substance  during  any  elementary 
change  must  be  the  sum  of  the  variation  of  the  sensible  heat 
of  the  mass  and  of  the  latent  heats.  The  convertibility  of  the 
thermal  unit  into  the  mechanical  unit  of  work  or  energy  renders 
it  a  matter  of  indifference  which  unit  is  adopted.  If  Q  repre- 
sent heat  measured  in  thermal  and  H  the  same  quantity  in 
mechanical  units,  and  if./  be  taken  as  the  symbol  of  the  me- 
chanical equivalent  of  heat,  and  A  —  -j.  the  thermal  equivalent 

of  the  mechanical  unit,  we  may  write  at  once,  as  the  expression 
of  the  first  law  of  thermodynamics, 

(i) 


246  THE   STEAM-BOILER. 

in  which  equation  K  is  the  dynamical  specific  heat,  or  in  sym- 
bols CJ,  the  product  of  the  thermally  measured  specific  heat, 
C,  by  Joule's  equivalent  ;  T  the  absolute  temperature  ;  5  the 
sensible  and  W^the  total  latent  heat,  measured  in  mechanical 
units. 

Hereafter  all  measurements  will  be  given  in  mechanical 
units,  unless  otherwise  stated. 

Separating  the  heat  doing  the  work,  W,  as  distinguished 
from  other  heat,  into  two  parts,  the  one,  Z,  the  internal  latent 
heat,  the  other,  U,  the  latent  heat  of  external  work, 


(2) 


and  making  the  "  internal  energy,"  as  it  is  sometimes   called,, 
£,  the  sum  of  the  sensible  heat  and  internal  work, 


Or,  otherwise  exhibited, 


dS  dW 


dL  dU 


dE  + 

And  these  expressions  are  true  for  all  substances  and   for  all 
possible  cases. 

The  sensible  heat  being  the  product  of  the  specific  heat  into 
the  range  of  temperature,  and  work  being  always  the  product 
of  the  alteration  of  volume  into  the  intensities  of  the  mean  re- 
sistance, the  preceding  equations  may  be  written  : 


-KdT^-pdv; 


HEAT  AS  ENERGY.  247 

when//,/,,  and  /  represent  respectively  the  internal,  the  ex- 
ternal, and  the  sum  of  internal  and  external  forces,  and  v  is  the 
volume  of  the  mass,  which  is  assumed  to  have  unity  of  weight. 
When,  as  here,  the  two  independent  variables  are  tempera- 
ture and  volume, 


(5) 


and,  from  the  preceding,  we  thus  find 


dH  _  dH 

~Tn^  —  A;    —j  —  —  P  \    ......    (6) 

dT  dv       * 


and  the  values  correspond  with  the  definitions  already  given. 

117.  The  Application  of  the  Second  Law  of  Thermo- 
dynamics establishes  some  important  modifications  of  the 
equations  just  derived.  Since  every  effect  is  proportional  to 
the  quantity  of  heat  acting  to  produce  it,  and  hence  to  the  ab- 
solute temperature  of  the  mass, 


(i) 


in  which  expression  Q  is  that  "  thermodynamic  function"  which, 
being  multiplied  by  the  absolute  temperature,  will  give  a  prod- 
uct measuring  the  quantity  of  heat  demanded  or  rejected  in  the 
production  of  the  change.  Again,  since  dW  —  pdv,  and  since, 
according  to  the  second  law,  the  total  pressure,/,  must  be  equal 
to  the  product  of  the  absolute  temperature  at  which  the  change 
occurs  by  the  rate  of  variation  of  pressure  with  temperature, 
dp 
dT' 


dH=  TdQ  =  KdT+  TdT;  .    .    ,    .    (2) 


and   the  form  and  value  of  the  thermodynamic  function  be- 
comes at  once  determinable  : 


248  THE   STEAM-BOILER. 

~^rd<v (3) 


By  a  process  which  need  not  be  here  described,  and  which 
can  be  seen  in  every  treatise  on  thermodynamics,  an  equation 
of  somewhat  similar  form,  but  in  which  the  variables  taken  are 
T  and/,  is  obtained,  thus: 


dH=  TdQ  =  KpdT-  Tdp;  .     ...     (4) 

(5) 


The  fundamental  equations  of  thermodynamics  are  thus 
completely  established.  As  here  given  they  are  general,  and 
applicable  to  all  substances.  In  the  present  work,  however, 
we  are  only  concerned  with  their  application  to  the  operation 
of  thermodynamic  changes  occurring  in  water  and  steam. 

118.  The  Computation  of  Internal  Forces  and  Work, 
and  of  external  work,  are  now  easily  effected.  Notwithstand- 
ing the  fact,  as  already  stated,  that  the  molecular  forces,  and 
the  work  performed  by  or  against  them,  are  beyond  the  reach 
of  any  physical  apparatus  and  are  incapable  of  direct  measure- 
ment, it  becomes  easy  to  calculate  both  force  and  work  from 
measurable  data  by  application  of  the  second  law  of  thermo- 
dynamics. 

The  rate  of  variation  of  external  pressure  and  work  with 
temperature,  at  constant  volume,  may  be  determined  easily  by 
experiment ;  this  rate,  according  to  the  second  law,  is  constant 
for  all  temperatures,  and  hence,  being  multiplied  by  the  abso- 
lute temperature  at  which  the  total  pressure  or  the  work  is  to 
be  determined,  the  product  measures  that  total  pressure  or 
work.  In  symbols,  let/,  wy  and  T  represent  the  total  pressure 
and  work,  and  the  absolute  temperature ;  then  the  rates  of  va- 

dp    div 
nation    -j^,,  -r=,,  with  temperature  may  be  ascertained  by,  for 


HEAT  AS  ENERGY.  249 

example,  noting  the  change  of  external  pressure,  as  measured 
by  the  steam-gauge,  for  a  change  of  one  degree  or  other  small 
but  exactly  measurable  range,  and  taking  this  ratio  of  differences, 

Ap  dp 

-jpr,  as  sensibly  equal  to  -j~.      The  work-ratio  is  obtained  by 

multiplying  the  Ap  by  the  volume   and  taking  this  product, 

Aw       dw 
Ap-v  =  Aw,  as  the  numerator  in  ~'=  ~T--      Then   the    total 


pressure,  internal  and  external,  must  be  measured  by 

.        f        t=TTf  .........   (0 

and  the  total  work  of  expansion  from  zero 


It  thus  becomes  possible  readily  to  determine  the  inter- 
nal and  external  pressures,  the  internal  and  external  work,  and 
the  latent  heats  of  the  vapors,  or  of  any  other  imperfectly 
gaseous  or  non-gaseous  substance. 

Since  the  heat  rendered  latent,  in  any  case,  is  the  equivalent 
of  the  work  performed  by  it,  the  latent  heat  of  vaporization 
must  be  exactly  equal,  dynamically,  to  the  work  just  measured, 
and  if  it  be  called  H  for  unity  of  weight, 


(3) 


when  Av  is  the  increase  of  volume  taking  place  during  the 
change  of  physical  state.  If  the  value  is  made  known,  as  is 
usual,  by  experiment,  and  Av  is  observed,  it  becomes  easy  to 
obtain 

dp       T(vt  -  v  ,) 
dT~     ~~H~ 

The  value  of  -IL  is  sometimes  found  to  be  negative,  e.g.,  in 


250  THE   STEAM-BOILER. 

the  case  of  ice.     Professor  James  Thomson  found 

—  ~—  o°.oi33  Fahr.  =  o°.oo74  Cent. 


as  the  amount  by  which  the  melting-point  of  ice  is  lowered  by 
every  increase  of  one  atmosphere  of  pressure.  The  latent  heat 
of  fusion  is  similarly  measured.  The  total  heat  of  vaporiza- 
tion, as  it  is  called,  from  a  temperature  Tl  and  at  a  tempera- 
ture TV  is  the  sum  of  the  latent  heat  converted  into  work,  as 
just  measured,  and  the  sensible  heat  demanded  to  raise  the 
temperature  from  Tl  to  T^. 

The  latent  heat  of  vaporization  per  unit  of  volume  is  ob- 
viously measured  by 

==      J. 


.         7T-M 

—  vl          dT 


and  this  permits  the  ready  calculation  of  the  heat  demanded  in 
supplying  any  steam,  or  other  vapor,  engine  with  the  quantity 
of  fluid  required  to  do  any  given  amount  of  work,  or  to  drive 
its  piston  through  any  given  space,  and  this  without  knowing 
the  density  of  the  fluid.  The  rate  of  variation  of  the  pressure 
of  the  vapor  at  the  boiling-point,  with  temperature,  may  be 
obtained  from  the  tables,  or  from  formulas  such  as  have  been 
given  for  steam  by  Regnault,  and  for  that  and  other  vapors  by 
Rankine.*  The  latter  are  the  most  general  and  usually  the 
most  exact  ;  they  have  the  form 


(6) 
whence 

O.      ...    (7) 


The  density  of  vapor  may  thus  be  readily  computed  from 
the  known  value  of  its  latent  heat,  and  much  more  satisfactorily 

*  Steam-engine,  §  206,  Div.  III. 


HEA  T  AS  ENERGY.  25  I 

and  exactly  than  it  can  be  derived  by  any  known  method  of 
experimental  determination.  The  increase  of  volume  of  unity 
of  weight  must  always  be 

»,-*,  =  £; (8) 

in  which,  practically,  the  values  of  vl  may  usually  be  neglected. 
Then  the  density*  is 


*  Tables  thus  calculated  for  steam  and  for  ether  and  other  fluids  are  given  by 
Rankine  in  his  Miscellaneous  Papers  and  in  his  treatise  on  the  Steam-engine. 


CHAPTER   VI. 

STEAM  AND   ITS   PROPERTIES. 

119.  The  Production  and  Use  of  Steam  involves  so  im- 
portant and  interesting  a  series  of  physical  phenomena  that 
they  are  deserving  of  special  study.  The  generation  of  steam, 
and  its  supply  to  the  steam-engine  or  other  apparatus  in  which 
it  finds  application,  is  a  process:  first,  of  heating  the  "  feed- 
water"  from  the  temperature  at  which  it  is  supplied  up  to  that 
at  which  it  is  vaporized ;  secondly,  the  change  of  its  physical 
state  at  the  latter  temperature;  thirdly,  its  expansion  into  a 
vapor;  and  finally,  in  some  cases,  the  drying  and  even  the 
superheating  of  the  steam  so  formed  until  it  assumes  the  truly 
gaseous  state. 

The  water  supplied  to  the  steam-boiler  often  comes  from 
rivers  or  smaller  streams,  sometimes  from  springs,  occasionally 
from  rain-water  cisterns,  and,  at  sea,  either  from  condensers  or 
stills,  or  from  the  ocean.  Each  one  of  these  sources  of  supply 
provides  water  having  properties  characteristic  of  its  origin,  and 
fitting  it,  or  unfitting  it,  as  the  case  may  be,  more  or  less  per- 
fectly for  its  use  in  the  boiler.  The  study  of  the  properties  of 
pure  water,  of  its  composition  and  chemical  and  physical  char- 
acter, and  of  the  nature  and  effects  of  the  impurities  dissolved 
or  mechanically  suspended  in  it,  is  thus  made  essential  to  an 
intelligent  understanding  of  the  problems  presented  to  the 
engineer  who  designs,  builds,  or  operates  the  steam-boiler. 
The  chemistry  and  physics  of  water  and  steam,  and  of  their 
changes  of  state  and  properties,  must  be  studied  in  connection 
with  the  thermodynamics  of  steam  in  its  application  as  a  vehicle 
and  a  reservoir  of  heat-energy;  and  with  this  study  must  be 
combined  also,  and  especially,  that  of  the  relations  of  heat  and 
steam  to  mechanical  power  as  developed  by  transformation  of 
heat  in  the  steam-engine.  This  latter  division  of  the  subject  is 
commonly  reserved  for  treatises  on  the  steam-engine. 


STEAM  AND  ITS  PROPERTIES.  253 

120.  The  Properties  of  Water,  as  noted  by  the  senses,  are 
familiar  to  all.  It  occurs  universally  distributed  throughout  the 
world,  in  earth,  air,  and  sea,  in  its  three  forms,  ice,  water,  and 
vapor,  and  in  its  most  common  and  familiar  form  covers  three 
fourths  of  the  surface  of  the  globe.  As  ice  and  snow  it  per- 
manently covers  the  arctic  regions  and  the  tops  of  lofty  moun- 
tains, and  as  vapor  it  forms  an  important  constituent  of  the 
atmosphere.  When  pure,  it  is  absolutely  free  from  either  taste 
or  smell,  and  is  colorless,  except  that  in  very  large  masses  it 
assumes  a  beautiful  blue  tint.  In  the  form  of  ice  it  weighs 
about  55  pounds  per  cubic  foot  (0.9  kilog.  to  the  litre,  nearly), 
and  has  considerable  tenacity,  while  yet  capable  of  flow,  with 
breaking  up  and  "  regelation"  under  pressure. 

In  the  liquid  state  it  still  retains  considerable  cohesive 
force,  but  the  lack  of  polarity  among  its  molecules,  and  its  con- 
sequent instability  of  form,  so  modify  its  properties  that  this 
tenacity  cannot  be  perceived  except  by  the  adoption  of  special 
expedients  directed  to  that  end.  Converted  into  vapor  or 
steam,  it  assumes  all  the  characteristics  of  the  gases,  except  that, 
like  other  vapors,  at  temperatures  and  pressures  near  the  boil- 
ing-point it  gives  evidence  of  the  imperfection  of  its  gaseous 
state  by  more  rapid  variation  of  pressure  with  temperature  than 
the  laws  of  the  gases  would  indicate.  Heated  above  the  tem- 
perature of  its  boiling-point  it  rapidly  takes  on  the  properties 
of  a  true  gas,  and  conforms  to  the  laws  of  Boyle  and  Marriotte, 

PV 
and  of   Charles  and    Gay-Lussac,  and  the  expression    — -  = 

constant  then  becomes  sensibly  correct. 

Water  is  the  most  efficient  of  all  known  solvents,  and  under 
certain  conditions  dissolves  nearly  all  kinds  of  matter,  even  at- 
tacking glass  and  other  mineral  substances  at  high  temperatures 
and  pressures.  Its  action  on  metals  is  often  marked,  and  is 
sometimes  very  serious.  It  dissolves  lead  rather  freely,  so 
much  so  that  lead-poisoning  not  infrequently  occurs  from  the 
presence  of  that  metal  in  drinking-water  held  in  contact  with 
it.  The  presence  of  carbonic  acid  in  observable  amount,  how- 
ever, seems  essential  to  the  rapid  solution  of  lead,  as  it  invaria- 
bly is  in  oxidation.  The  lead  in  solder  is  dissolved  more  freely 


254 


THE   STEAM-BOILER. 


than  pure  lead  alone.  Water,  especially  when  containing  car- 
bonic acid,  dissolves  iron  and  copper  rather  freely ;  its  presence, 
either  as  liquid  or  as  vapor,  is  absolutely  essential  to  the  cor- 
rosion of  iron  ;  both  moisture  and  carbon  dioxide  are  invariably 
present  when  iron  "  rusts"  rapidly. 

Bunsen  gives  the  following  as  the  coefficient  of  absorption 
by  water  at  the  given  temperatures,  for  familiar  substances  :* 


TEMPERATURES. 

Cent.  o°. 
Fahr.  32°. 

10° 

50° 

20° 

68° 

O.OIQ3O 

O   OIQ3O 

O   OIQ3O 

Oxvcren 

o  04  114 

o  03250 

o  02838 

Nitrogen 

o  0203^ 

o  01607 

o  00403 

Atmospheric  air     .  . 

O   O2J.7I 

o  010^3 

o  01704 

Carbon  dioxide  

I    7067 

i  1  8.1  7 

O   QOI4. 

'*       monoxide  

o  03287 

O   O26^ 

o  02312 

Carb   hydrogen,  CH4  

O.OS44Q 

O.O4S72 

O.O34QQ 

C2H4  

Sulph         "                .         . 

0.2563 
437o6 

0.1837 

o  c8c8 

0.1488 
2    QO^3 

Ammonia    

IO4Q.6 

812  8 

6^4.    O 

121.  The  Composition  of  Water  and  its  chemistry  are 
well  understood  in  all  its  technical  relations.  Cavendish  showed 
its  constitution  by  synthesis  in  1781  ;  Humboldt  and  Gay-Lus- 
sac,  in  1805,  found  it  to  consist  of  one  volume  hydrogen  and 
two  volumes  oxygen ;  while  Berzelius  and  Dulong  determined 
its  proportions  by  weight,  hydrogen  one  and  oxygen  eight,  i.e., 


H2 

Molecular 
Weight. 

2 

Calculated. 
II  .  ill 

Berzelius 
and  Dulong. 

II.  I 

O 

16 

88.888 

88.9 

H20 


18 


IOO.O 


Dumas. 
II. II 


100.00 


Lavoisier  made  the  composition  of  water  one  of  the  bases  of 
his  new  system. 

Water  is  a  neutral  compound,  exhibiting,  when  pure,  neither 
acid  nor  alkaline  reaction  ;  but  so  freely  does  it  dissolve  sub- 
stances with  which  it  is  brought  in  contact,  that  it  is  rarely 
found  in  nature  absolutely  free  from  either  acidity  or  alkalinity. 
Its  presence  is  essential  to  nearly  all  the  chemical  operations  of 
nature,  as  well  as  in  the  laboratory. 


*  Methods  of  Gasometry. 


STEAM  A ND  ITS  PR OPER  TIE S.  255 

The  fluid  may  be  decomposed  in  either  of  several  ways,  as 
by  heat  alone,  a  process  of  "  dissociation"  of  its  elements  tak- 
ing place  at  between  2000°  and  4000°  Fahr.  (1100°  to  22oo°C), 
or  by  the  voltaic  current,  and  by  the  action  of  various  metals  or 
metalloids  at  high  temperatures,  when  the  substance  employed 
has  a  strong  affinity  for  the  oxygen,  as  have  carbon,  iron,  etc. 

Water  is  found  wherever  hydrogen  is  burned,  in  air  or  oxy- 
gen, either  alone  or  in  combination  with  other  elements.  It 
enters  into  combination  with  many  other  substances,  and  as 
water  of  crystallization,  for  example,  often  influences  the  char- 
acter of  the  compound  to  a  very  important  degree. 

122.  The  Sources  and  Purity  of  Water  demand  careful  at- 
tention from  the  engineer  proposing  to  use  it  in  the  production 
of  steam ;  since  the  presence  of  any  foreign  matter  is  always 
productive  of  some  and  sometimes  of  serious  difficulties,  and 
even  of  dangers.  Rain-water  is  the  purest  of  all  natural  waters  ; 
but  even  rain-water  contains  all  such  gaseous  substances  in 
solution  as  may  have  been  dissolved  in  its  fall  through  the  at- 
mosphere, and  such  minute  quantities  of  organic  and  other 
solid  matter  as  are  found  floating  in  the  air.  The  volume  of 
dissolved  gas  is  usually  about  25  parts  in  1000  of  water.  As 
oxygen  dissolves  more  freely  than  nitrogen,  their  proportions 
in  solution  differ  from  those  of  the  atmosphere,  averaging  not 
far  from  one  third  oxygen  and  two  thirds  nitrogen. 

Spring-waters  hold  in  solution  every  soluble  element  or  com- 
pound found  in  the  rocks  and  soils  through  which  they  flow. 
The  purest  of  them  are  those  "  soft"  waters  rising  from  gra- 
nitic formations  ;  those  of  limestone  districts  contain,  often,  con- 
siderable quantities  of  lime,  and  are  very  "  hard."  Spring-waters 
are  often  so  heavily  charged  with  dissolved  substances  as  to  be 
useless  for  domestic  or  manufacturing  purposes.  Good  spring- 
water  is,  however,  often  found  "  fresh"  and  pure,  and  such  water 
should  always  be  sought  for  use  as  "  feed-water"  for  steam-boil- 
ers. 

River-water  is  usually  purer  than  spring-waters,  even  although 
largely  consisting  of  such  waters.  The  dilution  of  the  stream  by 
surface-water,  the  precipitation  of  lime  and  other  salts  held  in 
solution  only  by  carbonic  acid,  which  is  set  free  on  exposure  to 


256  THE   STEAM-BOILER. 

the  atmosphere,  and  the  purifying  influences  of  the  atmosphere, 
all  together  may  very  greatly  reduce  the  proportion  of  impurity. 
River-water  is  apt  to  contain  more  organic  matter  than  does 
spring-water;  this  is  sometimes,  though  rarely,  dangerous  in 
boilers.  It  is  liable  to  contain  large  quantities  of  sand,  clay,  or 
other  kind  of  soil,  mechanically  suspended  ;  but  this  can  usually 
be  removed  sufficiently  well  by  filtering. 

A  water  carrying  a  considerable  amount  of  the  carbonate  of 
lime  and  other  alkalies  in  solution,  and  used  in  the  boilers  of 
locomotives  in  the  Mississippi  valley,  deposited  a  scale  having 
the  following  analysis : 

Iron  peroxide 5 . 700  per  cent. 

Silica .• 2.960  " 

Potassa 5-131 

Alumina 320 

Soda 2.137  " 

Sulphuric  acid 006  " 

Lime 24.760  " 

Magnesia ,.     8.294  " 

Carbonic  acid.    41.060  " 

The  effect  was  to  produce  some  leakage  and  marked  loss  of 
economy.  This  may  be  taken  as  a  fair  sample  of  the  incrusta- 
tion to  be  expected  in  limestone  districts. 

123.  Sea-water  is  a  "  mineral  water,"  strongly  saline,  con- 
siderably chlorinated,  and  slightly  alkaline.  The  composition 
of  the  water  of  the  ocean  differs  very  slightly  in  different  local- 
ities. It  contains  about  -£%  of  its  own  weight  of  salts,  mainly 
common  salt,  with  various  other  chlorides  and  bromides,  and 
some  gases. 

The  following  analysis  was  made  by  Von  Bibra : 

Sodium  chloride 1671 . 34 

Magnesium  chloride 199.66 

Sodium  bromide 31 . 16 

Potass,  sulphate 108 . 46 

Magnes.       "        34-99 

Calcium        "        93. 30 


Total  in  i  U.  S.  gallon 2138.91  grs., 

or  3.569  per  cent,  by  weight. 


STEAM  A ND  I TS  PR OPER  7 7ES.  2 5 / 

Forschammer  finds  for  each  100  parts  chlorine: 

SO4  Mg  Ca  Total. 

Maximum I4-5I  6.768  2.257  181.40 

Mean 14.26  6.642  2.114  181.10 

Minimum 13-98  6.570  2.050  180.60 

In  some  inland  seas,  as  the  Great  Salt  Lake  and  the  Dead 
Sea,  the  proportion  of  saline  matter  is  enormously  greater. 
Herapath  found  the  latter  to  contain  19.73  per  cent  solid  mat- 
ter, of  which  one  half  was  common  salt,  and  one  third  magne- 
sium chloride ;  the  next  largest  constituents  were  the  calcium 
and  potassium  chlorides  and  sodium  bromide. 

Deposits  from  sea-water,  and  from  any  other  water  contain- 
ing solid  matter  either  in  solution  or  suspended,  will  always 
occur  on  evaporating  the  water;  and  these  deposits  form  the  in- 
crustation and  sediment  which  endanger  the  steam-boiler  and 
reduce  the  efficiency  of  its  heating-surfaces.  They  are  pre- 
vented at  sea,  usually,  by  the  adoption  of  the  surface-condenser, 
or  by  the  process  of  "  pumping  and  blowing"  where  the  jet-con- 
denser is  employed,  and  when  the  sea-water  is  thus  unavoid- 
ably used  in  the  boiler.  This  will  be  referred  to  in  describing 
the  operation  and  management  of  the  marine  steam-boiler. 

The  salts  in  sea-water  are  not  precipitated  at  the  boiling- 
point ;  but,  in  a  concentrated  solution  at  217°  Fahr.  (102° 
Cent.),  sulphate  of  lime  begins  to  come  down,  and  at  the  tem- 
peratures customarily  met  with  in  marine  steam-boilers  it  is  all 
deposited.  A  saturated  solution  of  common  salt  is  obtained  at 
a  temperature  of  about  230°  Fahr.  (i  10°  Cent.) and  atone  tenth 
the  volume  of  the  sea-water,  the  salt  having  increased  in  its  per- 
centage from  3  to  30.  A  cubic  foot  of  sea-water  weighs  about 
64  pounds,  or  |-^  that  of  fresh  water,  the  one  measuring  35  and 
the  other  36  cubic  feet  to  the  ton,  nearly.  The  boiling-point  of 
salt  water  rises  about  i°.2  Fahr.  (o°.7  Cent.)  for  every  3  per 
cent  of  salt  added  up  to  the  point  of  saturation.  (See  §  126.) 

The  character  of  the  water  in  a  marine  steam-boiler,  after 
long  working,  and  with   the  usual  moderate  concentration,  is 
shown   by  analyses  made   for  the  Author  by  Dr.  Albert   R. 
Leeds,  the  report  on  which  was  as  follows : 
17 


258  THE  STEAM-BOILER. 

EXAMINATION  OF  WATERS  FROM  A  MARINE  BOILER,  WITH 
REFERENCE  TO  CAUSES  OF  RAPID  CORROSION  OF  HEATING- 
SURFACES. 

Samples. 
I.  Forward  end  of  boiler  ;  2,  after  end  of  boiler ;  3,  hot  well. 

Preliminary  Instructions  and  A  nalyscs. 

The  instructions  were  to  examine  for  organic  acids  and 
copper. 

All  the  organic  acids  that  could  possibly  occur  under  the 
circumstances  were  looked  for  in  Nos.  i,  2,  and  3.  None  pres- 
ent. 

Of  copper,  none  was  found  except  in  No.  i,  and  then  only 
a  trace  when  the  examination  was  repeated  on  a  larger  quan- 
tity of  liquid.  If  the  quantity  of  water  at  my  disposal  had 
not  been  so  limited,  a  similar  examination  of  No.  2  might  have 
revealed  a  trace  of  copper  in  it  also. 

These  results  being  inadequate  to  explain  the  causes  of  cor- 
rosion, the  following  analyses  were  required  : 

ANALYSES   OF   THREE   SAMPLES. 

Amount  of  Solid  Matter  in  Waters. 

1.  100  cubic  cent 4. 562  grammes. 

(Corresponding  to  about  6.1  oz.  in  i  U.  S.  gallon.) 

2.  100  cubic  cent,  contained 4.8386         " 

3.  100     "         "  "        0.2680         " 

Loss  by  Ignition. 

These  residues  were  obtained  by  drying  at  110°  C.  On  ig- 
nition, water  was  given  off,  and  a  partial  decomposition,  attended 
with  loss  of  chlorine,  ensued.  But  unlike  many  samples  of 
water,  the  loss  by  ignition  in  these  cases  is  not  to  be  attributed 
to  organic  matter  present. 

No.  i  lost 9 . 43  per  cent. 

"    2    " ...     6.01         " 

"    3    " 15.11 


STEAM  AND  ITS  PROPERTIES.  2$$ 

Results  of  Qualitative  Analysis. 

X.  2.  3. 

Organic  acids None.  None.  None. 

Chlorine Present.  Present.  Present. 

Ammonia None.  None.  None. 

Lime None.  Trace.  None. 

Magnesia Abundant.  Abundant.  Abundant. 

Oxide  of  iron None.  None.  None. 

Copper Trace.  None.  None. 

Sulphuric  acid Present.  Present.  Present. 

Sodium Large.  Large.  Large. 

Bromine,    j.  not  tested  for. 
Iodine,        » 

The  most  striking  feature  is  the  large  amounts  of  the  chlo- 
rides and  sulphates  of  the  alkalies  and  magnesium — more  espe- 
cially the  magnesium  salts. 

Specific  Gravities  and  other  Properties. 

Specific  gravity  of  No.  i 1.0300     15°  C. 

"  "         "         2 1.0309         " 

3 1.0030 

I  was  slightly  turbid  from  suspended  matter,  but  colorless  ; 
2,  turbid,  and  of  a  slightly  pinkish  color;  3,  colorless  and  clear. 

It  will  be  noticed  that  the  specific  gravities  of  Nos.  I  and  2 
are  somewhat  greater  than  the  average  specific  gravity  of  sea- 
water,  which  is  1.027. 

Corrosive  Properties  of  the  Water. 

Ex.  I. — A  galvanic  pair  was  made  of  a  plate  of  copper  and 
one  of  iron,  separated  below  but  in  contact  above  the  liquid. 
On  immersion  into  water  No.  i  hydrated  sesquioxide  of  iron 
was  rapidly  formed.  No  notable  deposit  of  copper  could  be 
detected  on  the  iron  plate,  and  no  trace  of  copper  in  the  liquid. 
If  the  minute  trace  of  copper  was  precipitated  out,  the  coating 
was  too  slight  to  be  visible. 

Ex.  2. — A  sheet  of  iron  alone  was  immersed  in  the  water  No. 
i  at  the  boiling-point.  Oxide  of  iron  was  formed,  but  in  much 
less  quantity  than  in  Ex.  I. 


260  THE   Sl^EAM-BOILER. 

Ex.  3. — A  galvanic  pair,  as  in  Ex.  i,  was  put  in  the  circuit 
of  a  galvanometer.  On  making  contact  a  large  deflection  took 
place,  showing  high  tension,  the  needle  coming  to  rest  with  a 
permanent  deflection  of  3°.  At  the  same  time  oxidation  of  the 
iron  went  on  rapidly. 

Conclusions. 

That  water  having  a  composition  as  above  given,  and  with- 
out organic  acids,  is  capable  of  producing  corrosion  of  the  iron  ; 
that  such  water,  when  it  is  the  exciting  fluid  in  a  galvanic  com- 
bination, one  element  of  which  is  iron,  the  other  copper,  pro- 
duces a  galvanic  current  of  notable  quantity  and  intensity. 
Under  such  circumstances  corrosion  of  the  iron  takes  place 
more  rapidly  than  when  iron  alone  is  in  contact  with  the  liquid. 

124.  Technical  Uses  and  manufacturing  operations  com- 
monly require  the  purest  possible  water.  In  the  steam-boiler, 
especially,  where  all  the  water  evaporated  necessarily  leaves 
behind  every  particle  of  solid  matter  held  in  solution  at  its  in- 
troduction, purity  of  the  fluid  is  of  great  importance.  Half  a 
ton  of  lime  "  scale"  has  been  taken  from  the  boiler  of  a  locomo- 
tive, and  the  Author  has  seen  several  tons  of  salt  and  scale  in  a 
large  marine  boiler  which  had  been  ruined  by  its  presence,  and 
the  consequent  destruction  of  its  furnace  and  furnace-flues  by 
overheating  and  oxidation.  Boiler  explosions  have  often  been 
caused  by  such  incrustations.  The  prevention  and  removal  of 
scale  is  a  matter  of  serious  importance  in  steam-boiler  manage- 
ment, and  will  be  considered  later.  It  may  be  stated  here  that 
various  chemical  reagents  are  relied  upon  to  produce  a  remov- 
able and  comparatively  safe  form  of  salt-deposit,  and  heating 
and  filtration  of  the  water  before  it  enters  the  boiler  are  usually 
the  best  preventives. 

Filtration  by  means  of  filter-beds  for  large  volumes  of 
water,  and  by  filtering  apparatus  of  various  kinds,  may  always 
be  relied  upon  to  remove  the  undissolved  solid  matter.  Filtra- 
tion is  often  combined  with  heating  and  sometimes  with  chem- 
ical treatment  in  the  purification  of  water. 

The  temperatures  at  which  calcareous  matters  are  precipi- 
tated in  ordinary  boiler  waters  are  as  follows : 


STEAM  AND  ITS  PROPERTIES.  26l 

Carbonates  of  lime,  between 176°  and  248°  Fahr.    (80°  to  120°  C.) 

Sulphates  of  lime,  between 284°  and  424°  Fahr.  (140°  to  218°  G.) 

Chlorides  of  magnesium,  between 212°  and  257°  Fahr.  {100°  to  124°  C.) 

Chlorides  of  sodium,  between   324°  and  364°  Fahr.  (160°  to  184°  C.) 

In  order  to  free  water  from  these  salts  it  must  consequently 
be  heated  to  the  above  temperatures. 

125.  Water-analysis  is  often  resorted  to  by  the  engineer 
to  determine  the  proportion  of  scale-forming  constituents  in 
water  to  be  used  in  steam-boilers.  The  determination  of  the 
specific  gravity  is  sometimes  a  first  step ;  but  the  variations 
from  that  of  pure  water  are  usually  too  slight  to  be  observable. 
Where  it  is  taken  it  is  best  done  by  weighing  on  the  chemist's 
balance.  Color  is  observed  by  filling  a  long  glass  tube,  cap- 
ping the  ends  with  plate  glass,  and  looking  through  it  at  a 
white  background,  beside  a  tube  similarly  prepared  containing 
pure  water.  The  smell  and  taste  are  noted,  both  cold  and 
warm,  and  the  water  is  tested  with  litmus-paper  to  detect  any 
acidity  or  alkalinity ;  should  the  paper  turn  blue,  and  again 
lose  the  color  on  exposure  to  the  air,  ammonia  is  indicated. 

The  total  dissolved  solid  matter  contained  is  ascertained  by 
evaporating  to  dryness,  after  filtration,  and  weighing  the  de- 
posit. The  final  drying  is  usually  completed  in  a  steam-bath 
at  the  boiling-point,  212°  F.  (100°  C.).  The  weight  of  fixed 
mineral  contents  is  then  estimated  by  igniting  until  all  organic 
matter  is  decomposed  and  its  carbon  burned  away,  and  the  loss 
of  weight  noted.  The  suspended  matter  may  be  weighed  from 
the  filters,  or  may  be  obtained  by  allowing  it  to  settle  in  a  still 
tank  or  large  bottle  until  the  water  is  perfectly  clear,  decanting 
and  weighing  after  drying. 

The  "hardness"  of  water  is  gauged  by  several  methods,  of 
which  Clark's  is  one  of  the  best.  It  depends  upon  the  fact  that 
when  water  is  pure  it  froths  when  shaken  up  with  an  alcoholic 
solution  of  soap ;  while  if  mineral  salts  are  present  it  remains 
free  from  "  suds"  until  a  considerably  increased  amount  of  soap 
is  introduced.  The  quantity  of  soap  required  to  produce  ob- 
servable frothing  is  a  fairly  good  gauge  of  the  hardness  of  the 
water.  This  hardness  is  measured  in  "  degrees,"  each  of  which 
is  equal  to  o.oi  gramme  of  calcic  carbonate,  or  its  equivalent, 


262  THE   STEAM-BOILER. 

to  the  litre,  i.e.,  one  part  in  100,000.  The  standard  solution  is 
made  by  dissolving  white  curd-soap  in  alcohol  of  0.92  s.  g., 
until  I oo  cubic  centimetres  will  make  a  froth  with  an  equal 
quantity  of  water  of  20°  hardness.  This  is  preserved  in  glass- 
stoppered  bottles,  and  sometimes  diluted  to  make  other  stan- 
dard solutions.  The  presence  of  a  considerable  proportion  of 
magnesian  salts  causes  the  indication  of  this  test  to  be  de- 
fective, giving  too  low  a  figure  for  the  hardness. 

Carbonates  precipitated  by  boiling  are  dried  and  weighed. 
Organic  matter  is  calcined  and  so  determined  roughly,  or  may 
be  measured  by  reaction  with  potassic  permanganate.  The 
amounts  of  the  several  solid  constituents  are  customarily  ex- 
pressed as  parts  in  1,000,000,  by  weight,  of  the  water ;  some- 
times as  grammes  in  the  litre,  and  also  as  grains  to  the  gallon: 
the  last  may  be  reduced  from  the  next  preceding  by  multiply- 
ing grammes  per  litre  by  0.07;  they  can  be  converted  into 
degrees  on  Clark's  scale  by  multiplying  by  0.7.  Cubic  centi- 
metres per  litre  may  be  converted  into  grains  per  gallon  by 
dividing  by  3.738. 

126.  The  Purification  of  Water  is  often  essential  both 
for  sanitary  and  commercial  purposes.  The  first  and  simplest 
process  of  purification  of  water  containing  dissolved  substances 
is  distillation.  The  liquid  is  boiled  in  closed  vessels,  and  the 
steam  conducted  into  a  condenser,  and  there  restored  to  the 
liquid  state  by  cooling.  All  salts  and  solid  matters  are  left  be- 
hind in  the  evaporating  vessel,  and  the  distilled  fluid  is  abso- 
lutely pure  if  the  process  is  conducted  in  vessels  of  insoluble 
metal  or  of  glass.  In  many  cases  the  lime  salts  are  precipitated 
by  simple  heating  without  vaporization,  the  solid  precipitate 
coating  the  surfaces  of  the  heater  or  the  stone  or  other  masses 
with  which  it  is  sometimes  partly  filled.  The  addition  of  com- 
mon washing  soda  is  better  than  the  use  of  the  nostrums  sold 
as  "scale  preventives."  The  safest  course  is  always  to  have 
the  water  analyzed,  and  thus  to  ascertain  the  best  method  of 
treatment.  Saccharine  and  amylaceous  matters  and  extractive 
substances  are  useful  in  preventing  the  deposition  of  lime  and 
magnesian  carbonates  in  a  hard  scale,  and  barium  chloride  is 
effective  in  a  similar  manner,  where  the  water  contains  calcic 


STEAM  AND  ITS  PROPERTIES.  263 

sulphate.  Water  may  be  purified  of  its  lime  salts,  the  lime 
being  held  in  solution  as  a  bicarbonate,  by  the  addition  of  lime- 
water,  which  takes  a  part  of  the  carbonic  acid  and  causes  com- 
plete precipitation.  This  process  has  been  used  in  the  purifi- 
cation of  feed-water  for  use  in  steam-boilers ;  but  the  great 
quantity  of  water  used  generally  makes  it  a  somewhat  expen- 
sive system.  M.  E.  Asselin  recommends  the  use  of  glycerine 
to  prevent  incrustation  in  steam-boilers. 

Glycerine  soluble  in  water  in  every  proportion  increases  the 
solubility  of  combinations  of  lime,  and  especially  of  the  sul- 
phate ;  it  appears  besides  to  form  with  these  combinations 
soluble  compounds.  When  the  quantity  of  lime  becomes  so 
great  that  it  can  no  longer  be  dissolved,  nor  form  with  the 
glycerine  soluble  combinations,  it  is  deposited  in  a  gelatinous 
substance,  which  never  adheres  to  the  surface  of  the  iron 
plates.  Moreover,  the  gelatinous  substances  thus  formed  are 
not  carried  with  the  steam  into  the  cylinder  of  the  engine. 

M.  Asselin  advises  the  employment  of  one  pound  of  gly- 
cerine for  every  300  or  400  pounds  of  coal  burnt,  fifteen- days' 
supply  being  introduced  at  once.  Glycerine  combines  with  all 
the  salts,  and  leaves  the  plates  perfectly  clean. 

Filtration,  as  has  been  already  stated,  is  the  process  by  which 
all  mechanically-suspended  matter  is  removed  from  water  (§  124). 

127.  The  Physical  Characteristics  of  Water,  when  pure, 
are  the  following:  Its  density  is  about  770  times  that  of  air,  and 
is  a  maximum  at  about  39°. 2  Fahr.  (4°  Cent.),  with  exceedingly 
slight  variation  through  ordinary  ranges  of  temperature.  This 
is  taken  as  unity,  and  as  a  standard  for  all  densimetric  determi- 
nations with  solids  or  liquids.  Water  is  perfectly  elastic  with 
a  very  great  modulus ;  at  low  temperatures  the  compressibility 
increasing  with  temperature,  and  decreasing  with  its  solution 
of  salts.  Grassi,  Amaury  and  Descamps,  and  Cailletet,  all 
find  the  coefficient  of  compressibility  at  mean  atmospheric 
temperature  to  be  0.000045  to  0.000046.  At  the  freezing- 
point  it  becomes  0.00005. 

On  the  application  of  heat,  water  expands  from  unity  to 
1.043, in  passing  from  the  freezing  to  the  boiling  point.  It  has 
a  very  high  heat-capacity,  which  is  taken  as  unity  in  comparing 


264 


THE   STEAM-BOILER. 


specific  heats  of  other  substances.  It  is  an  almost  perfect  non- 
conductor of  heat,  and  only  transfers  heat  readily  by  convec- 
tion. Its  conductivity  in  absolute  measure  is  about  0.002.  On 
reducing  its  temperature  to  32°  F.  (o°  C.)  water  freezes,  and 
the  ice  produced  has  a  specific  gravity,  when  solid  and  pure,  of 
0.92,  and  floats  on  the  surface  of  water  at  the  same  tempera- 
ture. The  expansion  observed  at  freezing  takes  place  with 
immense  force,  and  often  bursts  water-pipes  when  they  are 
frozen  up.  The  boiling-point  of  water,  under  atmospheric  pres- 
sure, is  at  212°  Fahr.  (100°  Cent.),  and  very  variable,  as  shown 
later,  with  change  of  pressure.  The  boiling-point  also  rises  with 
the  increase  of  density  by  the  solution  of  other  substances. 

One  cubic  foot  of  water  weighs  62.425  pounds  at  maximum 
density,  or  nearly  1000  ounces  (62.5  pounds).  The  cubic  metre 
weighs  1000  kilogrammes.  One  atmosphere  counterbalances  a 
column  of  water  33.95  feet  (10.35  m.)  high. 

The  following  table  gives  the  volume  and  weight  of  dis- 
tilled water  at  various  temperatures  : 


Temperature. 

Ratio  of 
volume  to 
that  of 
equal 
weight  at 
maximum 
density. 

Weight 
of  a 
cubic 
foot. 

Temperature. 

Ratio  of 
volume  to 
that  of 
equal 
weight  at 
maximum 
density. 

Weight 
of  a 
cubic 
foot. 

Temperature. 

Ratio  of 
volume  to 
that  of 
equal 
weight  at 
maximum 
density. 

Weight 
of  a 
cubic 
foot. 

Fahr. 

Lbs. 

Fahr. 

Lbs. 

Fahr. 

Lbs. 

32-° 

.000129 

62.417 

210.° 

i  .04226 

59-894 

390.° 

•15538 

54-030 

39-i 

.000000 

62.425 

212. 

1.04312 

59-707 

400. 

.  16366 

53-635 

40. 

.  000004 

62.423 

220. 

1.04668 

59.641 

410. 

.17218 

53-255 

50- 

.000253 

62  .  409 

230. 

1.05142 

S9-372 

420. 

.18090 

52  862 

60. 

.000929 

62.367 

240. 

i-05633 

59.096 

43°- 

.18982 

52-466 

70. 

.001981 

62.302 

250. 

1.06144 

58.812 

440. 

.19898 

52-065 

80. 

.00332 

62.218 

260. 

1.06679 

58.517 

450. 

.20833 

51.662 

90. 

.00492 

62  .  119 

270. 

1.07233 

58.214 

460. 

.21790 

51-256 

100. 

.00686 

62.000 

280. 

1.07809 

57-903 

470. 

.22767 

50.848 

no. 

.  00902 

61.867 

290. 

1.08405 

57.585 

480. 

.23766 

50-438 

I2O. 

.01143 

61  .720 

300. 

1.09023 

37-259 

490. 

•24785 

50.026 

130. 

.01411 

61.556 

310. 

i  .09661 

56.925 

500. 

.25828 

49.611 

140. 

.01690 

61.388 

320. 

1.10323 

56-584 

Sio- 

.26892 

49-I95 

I50. 

.01995 

61  .204 

33°- 

i  .  i  1005 

56.236 

520. 

•27975 

48-778 

160. 

.02324 

61  .007 

340. 

i  .  i  i  706 

55-883 

530. 

.  29080 

48  360 

170. 

.02671 

60.801 

350. 

1.12431 

55-523 

540. 

.  30204 

47.941 

1  80. 

•03033 

60.587 

360. 

1-13175 

55-I58 

550. 

•3*354 

47-521 

190. 

.03411 

60.366 

370. 

1.13942 

54-787 

200. 

.03807 

60.136 

38o. 

1.14729 

54-4" 

STEAM  AND  ITS  PROPERTIES.  265 

128.  Changes  of  Physical  State  from  ice  to  water,  or  from 
water  to  steam,  or  the  reverse,  are  brought  about  by  change  of 
temperature  and  pressure.     The  heating  of  ice  from  any  tem- 
perature below  freezing  up  to  its  melting-point  causes  an  ex- 
pansion  of  the  mass  and  the  conversion  of  a  part  of  the  heat 
supplied  in  the  performance  of  the  work  of  separation  of  mole- 
cules, and  in  less  degree  that  of  expansion  of  the  mass  against 
atmospheric  pressure.     At  the  melting-point  rise  in  tempera- 
ture ceases,  and  all  heat  received  is  transformed  into  the  work 
of  "  disgregation,"  as  Clausius  has  called  it,  until  such  a  separa- 
tion of  molecules  has  been  effected  that  stability  of  form  is 
lost  with  the  vanishing  of  the  visible  effect  of  the  polarizing 
forces,  and  the  mass  becomes  liquid.     This  change  of  physical 
condition  having  been   effected,   the   addition    of   heat   again 
causes  rise  in   temperature,  until  a  second  halt  takes  place  ajt 
the  boiling-point  and  a  second  change  of  state  produces  vapori- 
zation.    Above  this  latter  point,  the  boiling-point,  the  absorp- 
tion of  heat  once  more  causes  increase  of  temperature.     There 
are  thus   two  marked  phenomena  to  be  noted  in  applying  heat 
to  this  substance,  and  at  every  stage   the  heat-supply  is  to  be 
observed   and  compared  with  the  amount   of  heating  and  of 
work  done  internally  and  externally ;  the  two  quantities,  that 
received  and  the  sum   of  these   expenditures,   will  always   be 
found  to  balance. 

129.  The  "  Critical  Point"  is  that  at  which  the  fluid  is  in- 
differently liquid   or  vapor  at   the  same  temperature  and  the 
same  pressure.     As  the  pressure  increases  and  temperature  rises, 
the  quantity  of  heat  rendered  "  latent"  by  conversion  into  the 
work  of  vaporization  decreases,  and  with  probably  every  fluid 
a  point  is  finally  reached  at  which  a  critical  set  of  conditions  is 
attained,  the  latent  heat  of  expansion  becoming  zero,  and  the 
body  exhibiting  the  properties  of  the  liquid  or  of  the  vapor  ac- 
cordingly as  it  is  above  or  below  this  point  on  the  thermometric 
and  pressure  scales.     M.  Cagniard  de  la  Tour  in  1822  first  ob- 
served that,  on  raising  the  temperature  of  a  confined  fluid,  part- 
ly liquid  and  partly  gaseous,  a  point  might  be  reached  at  which 
the  whole  mass  suddenly  became  homogeneous  in  appearance ; 
and  he  supposed  the  action  that  of  sudden  gasification.     Fara- 


266  THE   STEAM-BOILER. 

day  found,  a  year  later,  as  he  stated  it,  that,  above  a  certain 
temperature,  definite  for  each  case,  no  amount  of  pressure  would 
cause  liquefaction  of  a  vapor ;  and  Dr.  Andrews,  who  studied 
the  phenomenon  very  carefully,  finally  concluded  that  at  this 
"  critical  "  point  the  properties  of  the  two  forms  of  matter 
blended — that  the  one  passes  into  the  other  without  interrup- 
tion of  continuity  ;  these  physical  states  being  thus  found  to  be 
separate  forms  of  the  same  condition  of  matter.  M.  de  la  Tour 
reported  several  critical  temperatures  and  pressures,  thus : 


Temperature. 

Pressure 
Atmos. 

Ether     

•360°   <;  F        187°   t;  C 

07   c 

Alcohol   

407°   e.  F        2t;80  *  C 

IIQ    O 

Carbon  disulphide  

504.°  .  *  F.      262°  *  C 

66  5 

Water  

77^°.  O  F.       411°,  7  C 

? 

At  a  temperature  and  pressure  near  that  above  given 
water  dissolved  glass.  Steam  in  this  condition,  or  of  higher 
temperature  and  pressure,  being  worked  in  the  steam-engine, 
would  superheat  while  expanding ;  at  ordinary  temperatures 
and  pressures,  and  below  this  critical  state,  it  partially  condenses 
while  expanding  behind  a  piston,  and  thus  performing  work — 
a  fact  predicted  by  Rankine  and  Clausius  in  1849,  before  its 
experimental  discovery. 

Isothermal  lines  of  temperatures  considerably  above  those 
of  the  critical  points  for  the  various  pressures  are  sensibly  hy- 
perbolic; but  as  these  critical  pressures  and  temperatures  are 
approached  the  curve  becomes  distorted,  and  gives  a  combina- 
tion of  nearly  straight  lines  up  to  the  boiling-point,  a  perfectly 
straight  line  of  constant  pressure  and  variable  volume  during 
vaporization,  and  finally  it  is  hyperbolic  when  the  gaseous 
state  is  attained,  as  in  the  vaporization  of  water. 

Fig.  65  exhibits  a  set  of  isothermals  for  carbon  dioxide, 
as  drawn  from  Dr.  Andrews'  data.  The  dotted  lines  indicating 
the  probable  form,  as  suggested  by  Professor  James  Thomson,* 
of  portions  not  obtainable  from  those  data,  are  by  him  given  the 
Author,  as  shown.  Each  curve  relates  to  one  temperature,  and 

*  Rept.  Brit.  Assoc.  1871. 


STEAM  AND  ITS  PROPERTIES. 


267 


pressures  are  represented  by  the  horizontal  ordinates,  and  cor- 
responding volumes  of  mass  of  carbonic  acid  constant  through- 
out all  the  curves  are  represented  by  the  vertical  ordinates. 


FIG.  70. — ISOTHERMAL  CURVES.     CO2. 

Thomson  points  out  that,  by  experiments  of  Donny,  Dufour, 
and  others,  we  have  already  proof  that  a  continuation  of  the 
curve  for  the  liquid  state  past  the  boiling  stage  for  some  dis- 
tance, as  shown  dotted  in  Fig.  70,  from  a  to  some  point  b 
towards  /,  would  correspond  to  states  already  attained.  The 
overhanging  part  of  the  curve  from  e  to /may  represent  a  state 
in  which  there  would  be  unstable  equilibrium  ;  and  thus,  al- 
though the  curve  there  appears  to  have  some  important  theo- 
retical significance,  yet  the  states  represented  by  its  various 
points  would  be  unattainable  throughout  any  ordinary  mass  of 
the  fluid.  It  seems  to  represent  conditions  of  coexistent  tem- 
perature, pressure,  and  volume,  in  which,  if  all  parts  of  a  mass 
of  fluid  were  placed,  it  would  be  in  equilibrium,  but  out  of 
which  it  would  be  led  to  rush,  partly  into  the  rarer  state  of  gas, 
and  partly  into  the  denser  state  of  liquid,  by  the  slightest  in- 
equality of  temperature  or  of  density  in  any  part  relatively  to 
other  parts.  Above  this  point  the  fluid,  as  shown  by  the  hy- 


268  THE   STEAM-BOILER. 

perbolic  form  of  curve,  is  thoroughly  gaseous  ;  below  that  point 
it  may  be  called  vapor. 

130.  The  Spheroidal  State  of  water  is  that  condition  ob- 
served when  water  lies  in  contact  with  highly  heated  metal  sur- 
faces. When  so  situated,  a  liquid  does  not  wet  the  metal,  but  is 
supported  quite  out  of  contact  with  it  by  a  cushion  of  rapidly 
forming  vapor.  A  very  small  mass  assumes  the  form  of  a  drop, 
a  larger  quantity  that  of  a  sheet  of  liquid  of  continually  chang- 
ing outline.  The  supporting  "  Crookes's  layer,"  as  it  is  some- 
times called,  consists  of  particles  constantly  bounding  and  re- 
bounding between  the  adjacent  surfaces  of  fluid  and  metal,  and 
gradually  finding  their  way  out  of  that  capillary  space  as  their 
places  are  taken  by  newly  formed  particles  of  vapor.  Ether 
and  bromine  can  be  similarly  supported  on  the  surface  of  heated 
water,  and  ice  can  be  produced  in  a  red-hot  crucible  without 
contact.  On  cooling  the  metal,  a  temperature  is  finally  reached 
(356°  F.,  1 80°  C.)  at  which  contact  occurs,  and  an  explosion  often 
follows  from  the  suddeo  and  considerably  increased  evolution 
of  steam. 

This,  which  is  named,  from  its  discoverer,  Leidenfrost's  phe- 
nomenon, or,  otherwise,  the  "  caloric  paradox,"  has  been  very 
carefully  studied,  especially  by  Boutigny.  The  temperature  of 
the  spheroid  of  liquid  is  found  always  to  be  lower  than  its  boil- 
ing-point ;  contact  never  exists,  during  the  continuance  of  the 
phenomenon,  between  metal  and  liquid.  This  action  is  pro- 
moted by  any  conditions  which  tend  to  prevent  actual  contact 
and  wetting  of  the  metal  by  the  liquid,  a  fact  having  impor- 
tant bearing  on  the  special  danger  of  certain  forms  of  oily  or  of 
pulverulent  scale  in  steam-boilers.  This  interesting  and  im- 
portant action  is  illustrated  in  the  impunity  with  which  the  hand 
may  sometimes  be  dipped  in  molten  metal,  the  moisture  on  its 
surfaces  protecting  it  from  contact  and  injury. 

Superheated  water  or  other  liquid  may  be  sometimes  ob- 
tained by  careful  management,  as  in  the  experiments  of  Donny, 
Dufour,  and  others.  When  water  is  deprived  of  air  and  of  all 
impurities  it  may  be  raised  to  a  temperature  considerably  ex- 
ceeding the  boiling-point.  The  smaller  the  mass,  the  higher 
the  temperature  attainable.  M.  Donny  raised  water  in  a  closed 


STEAM  AND  ITS  PROPERTIES.  269 

glass  tube  to  248°  F.  (i  38°  C.),  when  explosive  ebullition  occurred, 
and  the  thermometer  dropped  to  212°  F.  (100°  C.).  Minute 
drops  (i  to  3  mm.  or  0.04  to  0.12  in.  in  diameter)  attained  346° 
F.  (i/5°  C.),  when  suspended  in  a  mixture  of  oils  of  its  own  den- 
sity, a  temperature  at  which  the  tension  of  steam  in  contact 
with  its  water  is,  under  normal  conditions,  between  8J  and  9 
atmospheres.  Water  in  glass  vessels  always  boils,  if  pure,  at 
a  temperature  slightly  exceeding  the  ordinary  boiling-point. 
Larger  masses  or  impure  water  are  not  easily  superheated. 
M.  Dufour  found  that  water  retains  the  liquid  state  more  per- 
sistently when  the  temperature  is  constant  and  pressure  is  made 
the  variable  than  when  the  contrary  conditions  are  arranged. 
MM.  Donny,  Dufour,  and  others  have  suggested  that  this  phe- 
nomenon may  be  a  frequent  cause  of  a  class  of  boiler-explosions 
known  as  "  fulminating,"  in  consequence  of  their  violence ;  and 
Mr.  Radley,  an  English  engineer,  reported  *  having  actually  su- 
perheated the  water  in  small  steam-boilers  27°  F.  (15°  C.)  above 
the  normal  boiling-point  for  the  pressure  at  which  they  were 
working.  On  the  other  hand,  Mons.  Hirsch,  the  well-known 
French  engineer  and  author,  reports  to  the  Commission  Centrale 
des  Machines  a  Vapeur  the  results  of  experiments  of  a  committee 
on  the  production  of  the  superheated  condition  in  the  water  of 
steam-boilers,  in  which,  studying  the  history  of  such  phenomena 
so  far  as  they  are  recorded,  and  conducting  a  somewhat  ex- 
tended series  of  experiments,  the  conclusion  was  finally  reached 
that  there  is  no  evidence,  up  to  the  present  time,  that  boiler 
explosions  may  be  caused  by  the  conditions  studied,  or  that 
such  conditions  ever  arise  in  practice.  If  they  occur  at  all,  it 
is  only  in  extremely  rare  instances,  and  as  a  consequence  of  a 
coincidence  of  circumstances  seldom  to  be  observed,  and  which 
are  neither  well  understood  nor  well  defined.  The  use  of  the 
thermometer  is  advised  to  determine  the  facts  bearing  upon 
this  question.  The  commission  to  which  the  report  is  made 
approve  and  adopt  these  conclusions. 

131.  Vaporization  of  water  or  other  liquid  has  been  seen  to 
be  a  process  of  conversion  of  sensible  heat-energy  into  the  so- 

*  Lond.  Mining  Journal,  June  28,  1856;  Scientific  American,  Aug.  2,  1856. 


270  THE   STEAM-BOILER. 

called  latent  form  by  transformation  into  work  in  the  separation 
of  molecules,  and  consequent  change  of  state  of  the  fluid.  This 
change  has  been  found  to  be  invariably  produced  at  a  tempera- 
ture fixed  for  every  pressure  under  normal  conditions,  and  to 
demand  a  certain  exact  and  determinable  quantity  of  heat. 
The  vapor  thus  formed,  so  long  as  it  is  in  contact  with  the 
liquid  from  which  it  issued,  retains  the  precise  temperature  of 
ebullition,  and  in  this  condition  the  steam  is  said  to  be  satu- 
rated. If  it  contains  no  unevaporated  moisture,  it  is  said  to 
be  dry  and  saturated.  It  is  capable  of  being  superheated  by 
isolation  and  further  addition  of  heat,  and  then  rapidly  assumes 
more  or  less  perfectly  the  gaseous  state.  M.  Hirn  found  that 
this  state  is  sensibly  reached  when  the  superheating  amounts 
to  anything  above  16°  F.  (9°  C).  The  fluid  is  known  in  this 
condition  as  "  steam-gas." 

The  specific  heat  of  superheated  steam  is  0.48,  equivalent 
to  371  foot-pounds,  at  constant  pressure,  and  is  0.37  (286  foot- 
pounds) at  constant  volume.  The  quantity  of  heat  doing  in- 
ternal work  here  becomes  insensible.  The  processes  of  conver- 
sion of  the  liquid  into  vapor  and  of  the  vapor  into  gas  are  seen 
to  be,  physically,  very  similar. 

132.  The  Thermal  and  Thermodynamic  Phenomena 
attending  the  production,  storage,  and  transfer  of  heat-energy 
through  the  vaporization  of  steam  are  evidently  in  some  sense 
identical  phenomena.  The  communication  of  heat  to  a  mass 
of  water  enclosed  in  a  steam-boiler  results  in  the  raising  of  its 
temperature,  the  expansion  of  the  mass,  the  performance  of 
work,  and  the  conversion  of  heat-energy  in  the  doing  of  that 
work.  The  boiling-point  is  simply  a  point  in  the  process  at 
which  the  proportion  in  which  the  heat  received  is  distributed 
to  its  several  purposes  is  altered,  and  the  superheating  of  steam 
is  the  result  of  passing  another  critical  period  in  the  process. 
The  principles  involved  and  these  phenomena  have  been 
already  fully  explained,  and  it  is  only  necessary  here  to  apply 
those  principles  and  the  data  obtained  by  experiment  to  the 
special  case  in  hand — the  production  and  use  of  steam.  It  is 
.perfectly  easy  to  determine  just  how  much  sensible  heat  is  em- 
ployed, untransformed,  in  raising  the  temperature  of  water  or 


STEAM  AND  ITS  PROPERTIES.  2/1 

steam  ;  how  much  is  transformed  in  producing  expansion,  and 
how  much  as  the  latent  heat  of  change  of  state. 

133.  Internal  Pressure  and  Work,  in  the  case  of  steam, 
will  illustrate   the  general  case  of  thermodynamic  change   as 
already  presented.     The  magnitude  of  the  molecular  resistance 
to  expansion  is  well  ascertained,  and  the  quantity  of  work  done 
in  overcoming  them  in  the  process  of  making  steam  is  as  easily 
determinate.     As  has  been  shown,  the  quantity  of  heat   be- 
coming latent  is  the  equivalent  of  this  internal  work,  and  the 
sum  of  the  latent  and  the  sensible  heat  absorbed  is  the  total 
heat  demanded  to  produce  the  change.     Both  may  be  deter- 
mined   by  the   processes  which   have  been  described    in  the 
earlier  chapters. 

134.  The  Computation  of  Internal  Work  or  of  internal 
pressure  has  been  seen  to  be  based  on  the  principle  expressed 
in  the  statement  of  the  second  law  of  thermodynamics. 

The  total  pressure,  internal  and  external,  at  any  tempera- 
ture, 7",  is  always 

*>=TTf  .........   CO 

The  rate  of  variation,  -j=,  of  pressure  as  a  function  of  tem- 

perature is  determined  experimentally,  and  the  value  of  this 
expression  may  be  obtained  from  the  expressions  already  given, 
or  from  the  tables  of  Regnault.  The  work  done  is  the  product 
of  their  total  pressure,  /,  into  the  alteration  of  volume,  Av,  or 


(2) 


Internal  pressure  and  work  are  completed  by  deducting  exter- 
nal pressure  and  work  from  these  totals. 

Clausius  thus  obtained  the  following  values  of/  for  steam 
of  the  pressures  given,  all  in  millimetres  of  mercury,  of  which 
760  measure  one  atmosphere  of  pressure  : 


2/2 


THE   STEAM-BOILER. 
TOTAL  PRESSURES  OF  STEAM. 


CENTIGRADE. 

EXTERNAL  PRESSURE. 

Ratio 

Total  Pressure 

Ratio 

dp 

P-T^- 

t. 

T. 

A- 

At. 

dT' 

*           dT' 

*' 

100° 

374° 

760 

I 

2/.2OO 

10146                 13.3 

120 

394 

1520 

2 

4S-595 

19150              12.6 

134 

408 

2280 

3 

67.020 

27277                   11-9 

144 

418 

3«-|0 

4 

34.345 

35172 

n.$ 

152 

426 

3800 

5 

100.375 

42659 

I  I  .  2 

159 

433 

4560 

6 

116.085 

50149 

II.O- 

166 

440 

5320 

7 

133-445 

58502 

10.8. 

171 

445 

6080 

8 

146.910 

65228 

10.7 

.176 

450 

6840 

9 

ioi  .27 

72410 

10.6. 

i  So 

454 

7600 

10 

173.425 

78561 

10.4 

199 

473 

II4OO 

15 

239-57 

II3077 

9-9' 

It  is  seen  that  the  rate  of  variation  of  pressure  with  the 
temperature  of  steam  continually  increases  as  pressures  and 
temperatures  rise,  and  that  the  proportion  of  internal  to  ex- 
ternal work  and  pressure  continually  diminishes  ;  but  that  the 
latter  ratio  is  large,  about  ten  to  one,  for  the  whole  range  of 
pressures  familiar  in  standard  practice. 

135.  The  Specific  Volume  of  steam,  or  the  volume  of 
unity  of  weight,  and  its  reciprocal,  the  density,  have  been  seen 
to  be  capable  of  easy  computation  when  the  latent  heat  of 
vaporization  at  the  given  temperature  is  known ;  since  this 
latent  heat  measures  the  work  done  while  the  force  resisting  it 
is  calculable  as  above.  From  the  expressions  already  given 

H        dp 
Av  =  ^f  +  dT'' 


a-  r 


we  thus  obtain  very  exact  values. 

Clausius  thus  obtains  the  following  values,  and  compares 
them  with  the  somewhat  uncertain  figures  of  Fairbairn  and 
Tate,  derived  experimentally.  Metric  m  easures  are  employed. 


t. 

T. 

A  v 
Calculated. 

By  Experiment. 

117.17 
124.17 
128.41 
137.46 
144.74 

398.17 
402.41 
411.46 
418.74 

0.947 
0.769 
0.681 

0.530 
0.437 

0.941 
0.758 
0.648 
0.514 
0.432 

STEAM  AND  ITS  PROPERTIES. 


273 


Quite  accurate  results  can  also  be  obtained  by  taking  the 
density  of  steam  as  0.622 ;  that  of  air  at  the  same  values  of  t 
and/  being  unity. 

The  volume  of  water  increases  with  temperature,  from  the 
temperature  of  maximum  density,  more  and  more  rapidly  as 
the  heat  is  increased.  The  following  are  the  values  as  given 
by  M.  Kopp,  who  experimentally  determined  them,  and  as  cor- 
rected by  Mr.  Porter  to  make  the  curve  exhibiting  the  data 
perfectly  smooth  : 


TEMPERATURE. 

VOLUMES  AS  PER 

Cent. 

Fahr. 

Kopp. 

Poiter. 

4° 

39°.  I 

.00000 

.  OOOOO 

5 

41  .0 

.00001 

.OOOO  I 

10 

50  .0 

.OOO25 

.00025 

20 

68  .0 

.00169 

.00171 

30 

86  .0 

.00423 

.00425 

40 

104  .0 

.00768 

.00767 

50 

122  .O 

.01190 

.01186 

60 

140  .0 

.01672 

.01678 

70 

158  .0 

.02238 

.02241 

80 

176  .O 

.02871 

.02872 

90 

194  .0 

•03553 

•03570 

IOO 

212  .O 

.04312 

.04332 

136.  Temperature,  Pressures,   and  Volumes  of  Steam 

are  related  by  natural  law  quite  as  definitely  as  those  governing 
these  relations  for  the  gases  ;  but  algebraic  expressions  of  those 
laws  are  not  yet  obtained,  except  empirically.  There  have  been 
numerous  formulas  proposed  of  the  latter  class,  some  of  which 
are  remarkably  exact  within  a  moderate  range.  The  most  ac- 
curate are  probably  those  of  Rankine,*  already  given  for  vapors 
generally : ' 

/?         C* 
A-  •          -— ; (I) 


- .  *  [•(= 


*  Steam-engine,  p.  237,  §206.     Ibid.,  pp.  559-5^4- 


18 


2/4  THE   STEAM-BOILER. 

in  which,  for  steam, 

B 
A  =  8.2591  ;         ££,=  0.003441  ; 

*, 

log  B  =  343642  ; 

7?2 

log  C  =  5-59873  ;      T^-8  =  o.ooooi  184  ; 

pressures  being  taken  in  pounds  on  the  square  foot  and  tem- 
perature in  degrees  Fahrenheit  on  the  absolute  scale.  The  ex- 
periments of  Regnault  and  of  Fairbairn  and  Tate  have  furnished 
the  generally  accepted  values. 

Unwin  has  proposed  *  a  simpler  formula  than  Rankine's, 
which,  while  not  quite  as   exact,  gives  more  manageable   ex- 

dp 
pressions  for  -      and  its  functions  ;  thus,  for  vapors  generally  : 


(3) 


i    dp  nb 

^ 

(a  — 


;.    ...    (5) 


t  dp  nb 

p  df  Tn 

=  2.30257*0  —  log/) (6) 

*  Phil.  Mag.,  April,  1886. 


STEAM  AND  ITS  PROPERTIES. 

For  steam,  these  formulas  become  : 


log/  =  7-5030--^;     .....     (7) 


/         7579         \'\ 
~  V-  5030  -log// 

i  dp       21815 


(7.5030  -log/)1'8.  .  . 


441.3 


=  2.8782(7.5030-  log  /);.     .     .  (10) 

which  expressions  give  remarkably  exact  results.  Metric  meas- 
ures are  used  throughout. 

137.  The  Specific  Heats  of  Water  and  Steam  vary 
somewhat  with  temperature  ;  this  variation  is  noted  with  all 
solids,  and  occurs  with  the  vapors,  although  in  vastly  less  de- 
gree ;  and  this  is  one  point  in  which  they  are  distinguished  from 
the  gases.  For  all  the  purposes  of  the  engineer  the  specific 
heat  of  either  saturated  steam  or  of  steam-gas  may  be  taken  at 
the  value  obtained  by  Regnault,  0.305,  the  quantity  of  heat,  in 
thermal  units,  demanded  to  raise  the  temperature  of  unity  of 
weight  of  saturated  steam  one  degree,  while  still  keeping  it 
saturated  by  the  evaporation  of  additional  water  ;  which  latter 
process  demands  the  transformation  of  0.695  unit  of  heat. 

The  specific  heat  of  isolated  steam-gas,  or  superheated 
steam,  is  given  by  Regnault  as  0.48051,  and  constant. 

The  specific  heat  of  water  was  determined  by  Regnault* 
very  carefully  and  exactly,  and  the  figures  so  obtained  have  been 

*Mem.  of  the  Academy  of  Sciences,  1847. 


276  THE   STEAM-BOILER. 

found  capable  of  being  very  accurately  represented  by  the  fol- 
lowing empirical  formula  of  Rankine  :* 

C—  i  -f  o.oooooo309(/  —  39°. i)2,    .     .    .    .    (i) 

in  which  t  is  the  temperature  on  the  common  Fahrenheit  scale. 
The  total  heat  demanded  from  /,  to  /„  would  thus  be 


h  =        Cdt  =  /3  —  /,  +  o.oooooo  1  03  [(V2  -  39°.  i)3 


and  the  mean  specific  heat  for  such  a  range  of  temperature  is 


+  ('1-39°.i)2]..          (3) 
On  the  Centigrade  scale  these  expressions  become 

C=^i+o.oooooi(t—  4°)",     .........    .    (10) 

*=/,-/H-o.oaxxx>33[(',-4T-(',-4°)1],     •    •    •    (*») 
~j  =  i  +  00000033K/.  -  4°)°  +  ('.  -  4°)C,  -  4°) 


The  specific  heat  of  ice  is  given  by  M.  Person  as  0.504. 

138.  The  Computation  of  Latent  and  Total  Heat  of 
Steam  is  readily  made  by  means  of  formulas  given  by  Reg- 
nault  or  based  upon  his  work,  which  covered  a  wide  range  of 
temperature  —  from  a  little  below  the  freezing-point  to  about 
375°  F.  (190°  C.).  The  following  is  the  formula  of  Regnault 
for  latent  heat  as  slightly  modified  and  corrected  by  Rankine 
for  the  British  and  metric  systems,  respectively  : 

/  =  1091.7  —  o.695(/  —  32°)  —  o.ooooooio3(/  —  39°.  i)3  ;     .    (i) 
4  =  606.5  —  0.695  1  —  0.000000333^  —  4°)3  ;  .....  (10) 


*  Trans.  Royal  Soc.  of  Edinburgh,  1851;  Steam  Engine,  p.  246. 


STEAM  AND   ITS  PROPERTIES.  277 

or,  approximately,  as  given  by  the  investigator, 

/  =   1092  -  o.7(/  —  32°) 
=     966  —  o.7(/  —  212) 

=    1147-0.7*.      ........      (2) 

lm—      606  —  0.7*  ......      ...  -(20) 

The  total  heat  of  evaporation  is  the  sum  of  the  latent  and 
sensible  heats,  and  may  be  taken  as 

k  =  Cfe-ig  +  4 

=   1091.7  +  o.305(f-  32°);      ....    (3) 
hm=  606.5  +0.305*;  .......    .(30) 

in  which  the  "  total  heat  "  measured  is  that  from  £,  at  t»  the 
original  temperature  of  the  water  and  that  of  evaporation,  and 
the  formulas  given  being  based  on  the  assumption  that  *,  is 
taken  at  the  melting-point  of  ice.  For  any  other  temperature 
the  following  will  give  satisfactorily  exact  measures  : 

h  =  1092  +  0.3ft  -  32)  -  ft  -  32°)  ; 

=   ii46  +  o.3ft-2i2)-ft-32°);   ...     (4) 
hm=  606.5+0.3*,  -*,;     .........  (4*) 

h  being  obtained  in  British  measures  and  hm  in  metric. 
For  steam-gas, 

h  =   1092  +  o.48ft  -  *,)  ........     (5) 

Professor  Unwin  proposes  the  following  for  the  latent  heat 
of  vaporization  of  steam  : 


4  =  799  ~ 


(7.5030  -  log/) 


0-8  ' 


which  is  found  to  be  extremely  exact.     He  also  obtains  for  the 
expansion  during  change  of  state, 


p  being  expressed,  as  above,  in  millimetres  of  mercury. 


278 


THE   S  TEA  M-B  OILER. 


139.  Factors  of  Evaporation  measure  the  relative  amount 
of  heat  demanded  to  effect  the  heating  of  water  from  a  given 
temperature,  tlt  and  its  vaporization  at  a  higher  temperature, 
t»  and  to  simply  produce  vaporization  at  the  boiling-point  un- 
der atmospheric  pressure,  which  latter  is  now  usually  taken  as  a 
standard.  The  value  of  this  factor  of  evaporation  is  evidently 


966.1 


-,  nearly.  .    (i) 


The   following   are   values   of   such   factors,   calculated   as 
above : 

TABLE  OF  FACTORS  OF  EVAPORATION. 


INITIAL  TEMPERATURE  OF  FEED-WATER,   7"a. 


FAHR. 

32° 

50° 

68° 

86° 

I 

04° 

22° 

] 

40° 

] 

58° 

I76° 

94° 

I2» 

212° 

.19 

•17 

•  15 

•13 

11 

.10 

.08 

.06 

.04 

.02 

.OO 

230 

.20 

.18 

.16 

.14 

12 

.10 

.08 

.06 

.04 

.02 

.01 

248 

.20 

.18 

16 

.14 

13 

.11 

.09 

.07 

.05 

.03 

.01 

266 

.21 

.19 

17 

•15 

13 

.11 

.09 

.07 

.06 

.04 

.02 

284 

.21 

.20 

18 

.16 

*4 

.  12 

.  IO 

.08 

.06 

.04 

.02 

302 

.22 

.20 

18 

.16 

.12 

.11 

.09 

.07 

•05 

•03 

320 

.22 

.21 

19 

.  17 

15 

•  *3 

.  ii 

.09 

.07 

•05 

•O3 

338 

•23 

.21 

.19 

•  I7 

15 

•14 

.12 

.10 

.08 

.06 

.04 

356 

•23 

.22 

.20 

.18 

16 

.14 

.  12 

.  IO 

.08 

.06 

.04 

374 
392 

.24 
.24 

.22 
•23 

.20 
.21 

.18 
.19 

17 

•15 

•13 

.11 

.  II 

.09 
.09 

.07 

.07 

:3 

410 

•25 

•23 

.22 

.20 

18 

!i6 

.14 

.12 

.  IO 

.08 

.06 

428 

•25 

•24 

.22 

.20 

18 

.16 

.14 

.12 

.  ii 

.09 

.07 

A  vastly  more  convenient  form  of  table  is  that  in  which  the 
pressures  at  which  evaporation  takes  place  are  given  ;  thus  : 


STEAM  AND   ITS  PROPERTIES.                             2JQ 

0      ^ 

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B  55 

280  THE    STEAM-BOILER. 

It  is  seen  that  the  relative  cost  of  using  feed-water  at  any- 
one temperature  as  compared  with  the  use  of  water  at  any 
other  temperature  is  as  the  reciprocal  of  their  factors  of  evapo- 
rization.  Thus  if  feed-water  can  be  supplied,  by  means  of  a 
heater,  at  210°  F.,  where  previously  drawn  from  the  mains  at 
50°,  the  relative  cost  of  making  steam  will  be,  at  100  pounds 
pressure,  by  gauge,  -j-fff  =  0.86,  and  a  gain  of  fourteen  per 
cent  will  be  effected.  As  will  be  seen  later,  these  tables  are 
very  useful  in  reducing  the  data  obtained  in  trials  of  steam- 
boilers  to  the  standard. 

140.  Regnault's  Researches  and  Methods  have  furnished 
all  the  essential  data  relating  to  tlie  production  of  steam  in  the 
boiler  and  the  supply  of  stored  heat-energy  to  the  engine. 

The  memoir  of  M.  Henri  Victor  Regnault  on  "  The  Elastic 
Forces  of  Aqueous  Vapors,"  *  in  which  he  described  his  re- 
searches, is  a  most  magnificent  exposition  of  a  still  more  re- 
markable series  of  investigations.  He  repeated  the  methods 
and  experiments  of  earlier  physicists,  invented  new  ways,  and 
finally  obtained  a  set  of  data  of  unexampled  extent  and  accu- 
racy .f  Regnault  found  that  the  density  of  aqueous  vapor  in 
vacua  and  under  feeble  pressure  may  be  calculated  according  to 
the  law  of  Boyle  and  Marriotte  when  the  fraction  of  saturation 
is  less  than  0.8,  while  the  density  becomes  sensibly  greater 
when  approaching  saturation.  He  further  found  that  the  den- 
sity of  vapor  in  air,  in  a  state  of  saturation,  may  be  similarly 
calculated,  and  the  ratio  of  weight  of  equal  volumes  of  vapor 
and  air  is  a  trifle  less  than  that  obtained  theoretically. 

The  data  obtained  by  Regnault  were  carefully  tabulated, 
and  curves  were  constructed  exhibiting  the  variation  of  pres- 
sure with  temperature  for  saturated  steam  for  the  whole  range 
covered  by  his  experiments.  Three  formulas  of  interpolation 
were  used  for  three  different  parts  of  the  scale  of  temperatures  ; 
for  that  part  below  the  freezing-point  he  adopted  the  formula 

£=*+&*',      .......     (i) 


*  Ann.  de   Chimie  et  de  Physique.,  July,  1844  ;  Mem.  de  1'Institut,  tome  xxi., 
p.  465  (1847)  ;    Mem.  de  1'  Academic  des  Sciences,  xxi.  xxvi. 
\  Vide  Dixon  on  Heat,  vol.  i..  §  724. 


STEAM  AND   ITS  PROPERTIES.  28  I 

in  which  F  is  the  pressure,  a  arid  b  constants,  and  ar  a  function 
of  T  —  t -\-  32°,  t  being  the  temperature  corresponding  to  F. 

Between  the  freezing  and  boiling  points  Regnault  used 
Biot's  formula, 

logF=a  +  &at  —  c0t; (2) 

and  above  the  boiling-point, 

log  F  =  a  —  bo?  —  cftT  ; (3) 

in  which  T  =  /  +  20.  This  last  answers  well,  also,  for  the  whole 
range.  In  it  0  =  6.2640348;  log  £  =  0.1397743;  log  c  = 
0.6924351  ;  log  a  —  1.994049292;  log  ft  =  1. 998343862,  as  given 
by  Regnault ;  or,  according  to  Dixon, 

a  —  6.263  509  686  5 
log  a  =  1.998  343  377  8 
log/?  =  1.994  048  173  7 
log  b  =  0.692  450  419  2 
log  c  =  0.139  553  958  4 

For  British  measures, 

a  =  4.859  984  524  7 
log  <*  =  1.999  079  751  3 
log/?  =  i".996  693  778  3 
log£  =  0.659  317  975  2 
log  c  =  0.020  517  432  4 

A  break  was  observed  by  Regnault,  and  is  exhibited  by  the 
curves  and  the  formulas,  at  the  freezing-point,  which  had  been 
attributed  to  error,  the  two  curves  cutting  each  other  at  a  very 
small  but  appreciable  angle  ;  but  Professor  James  Thomson 
has  supposed  such  a  break  to  have  a  real  existence,  and  to  be 
produced  by  the  physical  change  marking  the  freezing-point. 

141.  Regnault's  Tables  have  been  reproduced  in  many 
forms,  usually  with  additions.  The  Appendix,  among  other 
tables,  contains  the  data  obtained  by  Regnault  (Table  I.),  and 


282  THE   STEAM-BOILER. 

these  values  are  accepted  as  standard  universally.  The  table 
here  given  exhibits  the  temperatures  and  corresponding  pres- 
sures of  saturated  steam  throughout  the  full  range  now  used 
in  steam-boilers  and  far  beyond  ;  the  quantity  of  heat,  sensible 
and  latent,  in  unity  of  weight ;  the  total  heat  of  evaporation, 
and  the  density  of  the  steam.  Reference  to  these  tables  is 
vastly  more  convenient  than  calculation.  Should  it  be  neces- 
sary, or  desirable,  however,  to  make  such  calculations,  the  for- 
mulas already  given  will  furnish  the  means.  They  also  permit 
the  calculation  of  data  beyond  the  limits  of  Regnault's  experi- 
ment, and  are  probably  practically  correct  far  beyond  any  pres- 
sure likely  to  become  familiar  in  the  operation  of  steam-boilers. 
Regnault's  limit  was  at  230°  C.  (446°  F.).  Rankine's  formula 
has  been  used  beyond  it. 

The  formulas  used  in  these  calculations  are  elsewhere  given, 
but  are  here  grouped  for  convenience  of  reference.  British 
measures  are  used  throughout. 


77-5  PROPERTIES. 


283 


-t- 

i 

fc 

5 

% 

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c 

c. 

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1 

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n 

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2 

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c 

u 

1 

QUANTITY. 

Pounds  per  square  inch. 

1 

u 

1 

L, 

CO 

1 

Inches  of  mercury,  at  32°  Fahr. 

Feet  of  distilled  water,  at  temperature  of  r 
density. 

Atmospheres. 

Above  the  atmosphere,  in  pounds  per  square 

Fahrenheit's  scales. 

1 
•o 

'5 

a 
u 

1 

3 

1 

Required  to  raise  the  temperature  of  the  w 
32°  to  t°. 

Required  to  change  the  water  into  steam, 
latent  heat.) 

Required  to  overcome  the  pressure  of  the  su 
medium.  (External  latent  heat.) 

c 

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Total  heat  of  evaporation  above  32' 

'otal  heat  of  evaporation  per  pound  of  steam,  a 
in  units  of  evaporation. 

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284 


THE   STEAM-BOILER. 


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FORMULAS  RELATI: 

QUANTITY. 

t  heat  of  evaporation,  per  cu 

a  cubic  foot  of  steam,  in  pou 

of  distilled  water,  in  pounds, 

f  a  pound  of  steam,  in  cubic  I 

of  steam  to  volume  of  equal 
at  temperature  of  maximum 

of  distilled  water,  at  tempen 
:ight  at  temperature  of  maxii 

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fe 

STEAM  AND  ITS  PROPERTIES.  285 

142.  The  Stored  Energy  in  Steam  at  any  pressure  and 
temperature  is  now  easily  ascertained  by  calculation,  in  accord- 
ance with  the  first  law  of  thermodynamics. 

The  first  attempt  to  calculate  the  amount  of  energy  latent 
in  the  water  contained  in  steam-boilers,  and  capable  of  greater 
or  less  utilization  in  expansion  by  explosion,  was  made  by  Mr. 
George  Biddle  Airy,*  the  Astronomer  Royal  of  Great  Britain, 
in  the  year  1863,  and  by  the  late  Professor  Rankinef  at  about 
the  same  time. 

Approximate  empirical  expressions  are  given  by  the  latter 
for  the  calculation  of  the  energy  and  of  the  ultimate  volumes 
assumed  by  unit  weight  of  water  during  expansion,  as  follows, 
in  British  and  in  metric  measures  : 


_  _  423.55(^-100)' 

T+  1  134.4  r+648 

_  3676(^-212)  2.29(^-100) 

T+  11344  T+648 

These  formulas  give  the  energy  in  foot-pounds  and  kilo- 
grammetres,  and  the  volumes  in  cubic  feet  and  cubic  metres. 
They  may  be  used  for  temperatures  not  found  in  the  tables  to 
be  given,  but,  in  view  of  the  completeness  of  the  latter,  it  will 
probably  be  seldom  necessary  for  the  engineer  to  resort  to 
them. 

The  quantity  of  work  and  of  energy  which  may  be  liberated 
by  the  explosion,  or  utilized  by  the  expansion,  of  a  mass  of 
mingled  steam  and  water  has  been  shown  by  Rankine  and  by 
Clausius,  who  determined  this  quantity  almost  simultaneously, 
to  be  easily  expressed  in  terms  of  the  two  temperatures  be- 
tween which  the  expansion  takes  place. 

When  a  mass  of  steam,  originally  dry,  but  saturated,  so 
expands  from  an  initial  absolute  temperature,  TJt  to  a  final 
absolute  temperature,  T»  if  /is  the  mechanical  equivalent  of 
the  unit  of  heat,  and  H  is  the  measure,  in  the  same  units,  of 

*"  Numerical    Expression  of  the    Destructive    Energy  in  the  Explosions  of 
Steam  Boilers." 

f  "  On  the  Expansive  Energy  of  Heated  Water." 


286  THE   STEAM-BOILER. 

the  latent  heat  per  unit  of  weight  of  steam,  the  total  quantity 
of  energy  exerted  against  the  piston  of  a  non-condensing  en- 
gine, by  unity  of  weight  of  the  expanding  mass,  is,  as  a  maxi- 
mum, 


log       +  -#.     .     .    (A) 


This  equation  was  published  by  Rankine  a  generation  ago.* 

When  a  mingled    mass  of   steam  and  water  similarly  ex- 

pands, if  M  represents  the  weight  of  the  total  mass  and  m  is 

the  weight   of  steam  alone,  the  work  done  by  such  expansion 

will  be  measured  by  the  expression, 


U=  MJT&  -  i  -  hyp  log  ^)  +  m  ^^H.       (B) 

X  -L  J-     '  J- 


This  equation  was  published  by  Clausius  in  substantially 
this  form.f 

It  is  evident  that  the  latent  heat  of  the  quantity  m,  which 
is  represented  by  mff,  becomes  zero  when  the  mass  consists 
solely  of  water,  and  that  the  first  term  of  the  second  member 
of  the  equation  measures  the  amount  of  energy  of  heated  wa- 
ter which  may  be  set  free,  or  converted  into  mechanical  energy 
by  explosion.  The  available  energy  of  heated  water,  when 
explosion  occurs,  is  thus  easily  measurable. 

The  computers  of  the  tables  given  in  the  Appendix 
were  Messrs.  Ernest  H.  Foster,  and  Kenneth  Torrance. 
The  tables  range  from  20  pounds  per  square  inch  (1.4  kgs.  per 
sq.  cm.)  up  to  100,000  pounds  per  square  inch  (7030.83  kgs. 
per  sq.  cm.),  the  maximum  probably  falling  far  beyond  the  range 
of  possible  application,  its  temperature  exceeding  that  at  which 
the  metals  retain  their  tenacity,  and  in  some  cases  exceeding 
their  melting-points.  These  high  figures  are  not  to  be  taken 


*  Steam-engine  and  Prime  Movers,  p.  387. 

f  Mechanical  Theory  of  Heat,  Browne's  translation,  p.  283. 


STEAM  AND  ITS  PROPERTIES.  28? 

as  exact.  The  relation  of  temperature  to  pressure  is  obtained 
by  the  use  of  Rankine's  equation,  of  which  it  can  only  be  said 
that  it  is  wonderfully  exact  throughout  the  range  of  pressures 
within  which  experiment  has  extended,  and  within  which  it 
can  be  verified.  The  values  estimated  and  tabulated  are  prob- 
ably quite  exact  enough  for  the  present  purposes  of  even  the 
military  engineer  and  ordnance  officer.  The  form  of  the  equa- 
tion, and  of  the  curve  representing  the  law  of  variation  of 
pressure  with  temperature,  indicates  that,  if  exact  at  the 
familiar  pressures  and  temperatures,  it  is  not  likely  to  be  in- 
exact at  higher  pressures.  The  curve  at  its  upper  extremity 
becomes  nearly  rectilinear. 

The  table  presents  the  values  of  the  pressures  in  pounds 
per  square  inch  above  a  vacuum,  the  corresponding  reading  of 
the  steam-gauge  (allowing  a  barometric  pressure  of  14.7  pounds 
per  square  inch),  the  same  pressures  reckoned  in  atmospheres, 
the  corresponding  temperatures  as  given  by  the  Centigrade 
and  the  Fahrenheit  thermometers,  and  as  reckoned  both  from 
the  usual  and  the  absolute  zeros.  The  amount  of  the  available 
stored  energy  of  a  unit  weight  of  water,  of  the  latent  heat  in  a 
unit  weight  of  steam,  and  the  total  available  heat-energy  of 
the  steam,  are  given  for  each  of  the  stated  temperatures  and 
pressures  throughout  the  whole  range  in  British  measures, 
atmospheric  pressures  being  assumed  to  limit  expansion.  The 
values  of  the  latent  heats  are  taken  from  Regnault,  for  mode- 
rate pressures,  and  are  calculated  for  the  higher  pressures,  be- 
yond the  range  of  experiment,  by  the  use  of  Rankine's  modifi- 
cation of  Regnault's  formula. 

Studying  the  table,  the  most  remarkable  fact  noted  at  the 
lower  pressures  is  the  enormous  difference  in  the  amounts  of 
energy,  in  available  form,  contained  in  the  water  and  in  the 
steam,  and  between  the  energy  of  sensible  heat  and  that  of 
latent  heat,  the  sum  of  which  constitutes  the  total  energy  of 
the  steam.  At  20  pounds  per  square  inch  above  zero  (1.36 
atmos.),  the  water  contains  but  145.9  foot-pounds  per  pound  ; 
while  the  latent  heat  is  equivalent  to  16,872.9  foot-pounds,  or 
more  than  115  times  as  much;  i.e.,  the  steam1  contains  116 
times  as  much  energy  in  the  form  of  latent  heat  per  pound,  as 


288  THE   STEAM-BOILER. 

does  the  water,  from  which  it  is  formed,  at  the  same  tempera- 
ture. The  temperature  is  low  ;  but  the  amount  of  energy  ex- 
pended in  the  production  of  the  molecular  change  resulting  in 
the  conversion  of  the  water  into  steam  is  very  great,  in  conse- 
quence of  the  enormous  expansion  then  taking  place.  At  50 
pounds  the  ratio  is  20  to  I  ;  at  100  pounds  per  square  inch  it 
is  14  to  I,  at  500  it  is  5  to  I  ;  while  at  5000  pounds  the  energy 
of  latent  heat  is  but  1.4  that  of  the  sensible  heat.  The  two 
quantities  become  equal  at  about  7500  pounds.  At  the  high- 
est temperature  and  pressure  tabled,  the  same  law  would  make 
the  latent  heat  negative ;  it  is  of  course  uncertain  what  is  the 
fact  at  that  point. 

At  50  pounds  per  square  inch  the  energy  of  heated  water 
is  2550.4  foot-pounds,  while  that  of  the  steam  is  68,184,  or 
enough  to  raise  its  own  weight  to  a  height,  respectively,  of  a 
half-mile  and  of  12  miles.  At  75  pounds  the  figures  are  4816 
and  90,739,  or  equivalent  to  the  work  demanded  to  raise  the 
unit  weight  to  a  height  of  four  fifths,  and  of  about  17  miles  re- 
spectively. At  100  pounds  the  heights  are  over  one  mile  for 
the  water  and  above  20  miles  for  the  steam. 

Comparing  the  energy  of  water  and  of  steam  in  the  steam- 
boiler  with  that  of  gunpowder,  as  used  in  ordnance,  it  will  be 
found  that  at  high  pressures  the  former  become  possible  rivals 
of  the  latter.  The  energy  of  gunpowder  is  somewhat  variable 
with  composition  and  perfection  of  manufacture,  and  is  very 
variable  in  actual  use,  in  consequence  of  the  losses  in  ordnance 
due  to  leakage,  failure  of  combustion,  or  retarded  combustion 
in  the  gun.  Taking  its  value  at  what  the  Author  would  con- 
sider a  fair  figure,  250,000  foot-pounds  per  pound,  it  is  seen 
that,  as  found  by  Airy,  a  cubic  foot  of  heated  water,  under  a 
pressure  of  60  or  70  pounds  per  square  inch,  has  about  the  same 
energy  as  one  pound  of  gunpowder.  The  gunpowder  ex- 
ploded has  energy  sufficient  to  raise  its  own  weight  to  a  height 
of  nearly  50  miles,  while  the  water  has  enough  to  raise  its 
weight  about  one  sixtieth  that  height.  At  a  low  red  heat  wa- 
ter has  about  40  times  this  latter  amount  of  energy  in  a  form 
to  be  so  expended.  One  pound  of  steam,  at  60  pounds  pres- 
sure, has  about  one  third  the  energy  of  a  pound  of  gunpowder. 


STEAM  AND  ITS  PROPERTIES. 


289 


At  100  pounds  it  has  as  much  energy  as  two  fifths  of  a  pound 
of  powder,  and  at  higher  pressures  its  energy  increases  very  slowly. 

143.  The  Curves  of  Stored  Energy  are  most  instructive. 
Plotting  the  tabulated  figures  and  determining  the  form  of  the 


£  800 


1500* 
1100* 

300' 

?0tf» 
\ 

1100 
000° 

x? 

axf 


500 


00« 


1WW          20UO          8000          4000 


6000          7000          8000         9000         10000        11000        12000 


FIG.  71. — CURVE  OF  HEAT  IN 


curve  representing  the  law  of  variation  of  each  set,  we  obtain 
the  peculiar  set  of  diagrams  exhibited  in  the  accompanying  en- 
graving. In  Fig.  71  are  seen  the  curves  of  absolute  tempera- 


iq 


290 


THE   STEAM-BOILER. 


ture  and  of  latent  heat  as  varying  with  variation  of  pressure. 
They  are  smooth  and  beautifully  formed  lines,  having  no  rela- 
tion to  any  of  the  familiar  curves  of  the  text-books  on  co-ordi- 


875000 


300099 1 


£790001 


raooo 


128000 


w 


200000  O 


75000 


25000 


cool 


1000    2000    8000    4000    5000    6000    7000    8000    9000 

ABSOLUTE  PRESSURE  IN  FOOT  POUNDS  PER.  SQ.  IN. 

FIG.  72 — CURVE  OF  HEAT-ENERGY  IN  STEAM. 


10000       11000        UOQO 


nate  geometry.  In  Fig.  72  are  given  the  curves  of  available 
energy  of  the  water  of  latent  heat  and  of  steam.  The  first 
and  third  have  evident  kinship  with  the  two  curves  given  in 


STEAM  AND  ITS  PROPERTIES.  29! 

the  preceding  illustration ;  but  the  curve  of  energy  of  latent 
heat  is  of  an  entirely  different  kind,  and  is  not  only  peculiar  in 
its  variation  in  radius  of  curvature,  but  also  in  the  fact  of  pre- 
senting a  maximum  ordinate  at  an  early  point  in  its  course. 
This  maximum  is  found  at  a  pressure  of  about  one  ton  per 
square  inch— a  pressure  easily  attainable  by  the  engineer. 

Examining  the  equations  of  those  curves,  it  is  seen  that 
they  have  no  relation  to  the  conic  sections,  and  that  the  curve, 
the  peculiarities  of  which  are  here  noted,  is  symmetrical  about 
one  of  its  abscissas,  and  that  it  must  have,  if  the  expression 
holds  for  such  pressures,  another  point  of  contrary  flexure  at 
some  enormously  high  pressure  and  temperature.  The  for- 
mula is  not,  however,  a  "  rational  "  one,  and  it  is  by  no  means 
certain  that  the  curve  is  of  the  character  indicated  ;  although 
it  is  exceedingly  probable  that  it  may  be.  The  presence  of 
this  characteristic  point,  should  experiment  finally  confirm  the 
deduction  here  made,  will  be  likely  to  prove  interesting,  and 
it  may  be  important  ;  its  discovery  may  possibly  prove  to  be 
useful. 

The  curve  of  energy  of  steam  is  simply  the  curve  obtained 
by  the  superposition  of  one  of  the  two  preceding  curves  upon 
the  other.  It  rises  rapidly  at  first,  with  increase  of  tempera- 
ture, then  gradually  rises  more  slowly,  turning  gracefully  to 
the  right,  and  finally  becoming  nearly  rectilinear.  The  curve 
of  available  energy,  of  heated  water,  exhibits  similar  character- 
istics ;  but  its  curvature  is  more  gradual  and  more  uniform. 

144.  The  Actual  Power  of  Steam  and  of  Boilers  evi- 
dently depends  upon  the  efficiency  of  the  method  of  applica- 
tion, and  on  the  apparatus  employed.  The  quantity  of  heat- 
energy  supplied  to  the  engine  and  yielded  by  the  generator 
has  been  seen  to  be  easily  calculable  by  simply  multiplying  the 
quantity  of  heat  given  to  the  steam  by  the  fuel,  by  the  me- 
chanical equivalent  of  heat.  The  amount  available  as  energy 
may  be  the  total  quantity  so  supplied,  as  when  the  steam  is 
condensed  in  heating  buildings  or  otherwise,  and  is  returned  as 
feed-water  to  the  boilers  ;  or  it  may  be  any  less  amount,  ac- 
cordingly as  the  method  of  utilization  is  more  or  less  effective. 
The  tables  given  in  the  Appendix  furnish  the  data  for  calcu- 


THE   STEAM-BOILER. 

lation  in  any  case  in  which  the  efficiency  of  transfer  and  of 
transformation  is  known.  Where  no  constant  value  can  be 
assumed  for  the  efficiency  of  the  system  employed,  it  is  some- 
times, nevertheless,  found  to  be  important  to  establish  a  stand- 
ard conventionally.  Thus,  in  the  calculation  of  available 
stored  energy,  as  given  in  the  Appendix,  Table  II.,  it  was  as- 
sumed that  the  steam  would  be  expanded  to  atmospheric  pres- 
sure. Similarly,  convention  has  established  the  unit  horse- 
power of  steam-boilers,  in  order  to  afford  a  standard  of 
comparison  in  test-trials,  and  to  give  a  means  of  rating  boilers 
by  the  designer,  the  builder,  or  the  purchaser  and  user. 

The  operation  of  boilers  occurs  under  a  wide  range  of 
actual  conditions — the  steam-pressure,  the  temperature  of  feed- 
water,  the  rate  of  combustion  and  of  evaporation,  and,  in  fact, 
every  other  variable  condition,  differing  in  any  two  trials  to 
such  an  extent  that  direct  comparison  of  the  totals  obtained, 
as  a  matter  of  information  regarding  the  relative  value  of  the 
boilers,  or  of  the  fuel  used,  becomes  out  of  the  question.  It 
has  hence  gradually  come  to  be  the  custom  to  reduce  all  results 
to  the  common  standard  of  weight  of  water  evaporated  by  the 
unit-weight  of  fuel,  the  evaporation  being  considered  to  have 
taken  place  at  mean  atmospheric  pressure,  and  at  the  tempera- 
ture due  that  pressure,  the  feed-water  being  also  assumed  to 
have  been  supplied  at  the  same  temperature.  This,  in  techni- 
cal language,  is  said  to  be  the  "  equivalent  evaporation  from 
and  at  the  boiling-point"  (212°  Fahr.,  100°  C).  This  standard 
has  now  become  generally  incorporated  into  the  science  and 
the  practice  of  steam-engineering.  The  "  Unit  of  Evaporation  " 
is  one  pound  of  water  at  the  boiling-point,  evaporated  into 
steam  of  the  same  temperature.  This  is  equivalent  to  the 
utilization  of  965.7  British  thermal  units  per  pound  of  water  so 
evaporated.  The  economy  of  the  boiler  may  thus  be  expressed 
by  the  number  of  units  of  evaporation  obtained  per  pound  of 
combustible. 

145.  The  Horse-power  of  Steam-Boilers  must  always  be 
reckoned  on  an  assumed  basis  involving  the  amount  of  heat 
supplied  from  the  furnace,  the  conditions  determining  the 
availability  of  that  heat  as  stored,  and  the  circumstances  con- 


STEAM  AND  ITS  PROPERTIES.  293 

trolling  its  expenditure  and  transformation.  The  term  must 
evidently  be  purely  conventional  and  technical,  and  its  defini- 
tion must  be  strictly  limited. 

The  character  and  magnitude  of  the  unit  to  be  chosen  to 
express  the  "  power  "  of  the  steam-boiler  is  not  fully  settled, 
though  the  subject  has  attracted  much  attention  among  engi- 
neers. It  is  evident  that  since  the  boiler  is  merely  an  appara- 
tus for  the  generation  of  steam,  and  since  the  province  of  the 
steam-engine  is  to  develop  power  from  that  st^am,  and  with  a 
degree  of  efficiency  which  may  vary  enormously,  it  is  certain 
that  we  have  no  natural  unit  of  power  for  steam-boilers.  It 
may  even  be  asserted  that  no  natural  unit  can  exist.  The 
most  scientific  system  of  power-rating  yet  proposed  considers 
the  power  of  a  boiler  to  be  that  expended  by  it  in  driving  out 
all  the  steam  which  it  makes  against  the  pressure  of  the  atmos- 
phere, a  system  suggested  by  Nystrom.* 

The  weight  of  water  to  be  evaporated  per  hour  at  any 
given  pressure  to  produce  one  horse-power  as  the  equivalent  of 
its  natural  effect  without  expansion,  by  impelling  a  piston 
against  its  load,  is  calculable  with  sufficient  accuracy  by  the 
formula  of  Nystrom  : 


„  r 


.37484 


in  which  V  is  the  volume  of  steam  in  cubic  feet,  /  the  absolute 
pressure  in  pounds  per  square  inch,  and  v  the  volume  of  steam 
relatively  to  that  of  water  at  the  freezing-point.  By  this 
method  we  obtain  the  following  values  : 

*  Mechanics,  i8th  Ed.,  p.  562. 


294 


THE   STEAM-BOILER. 


p 

H.  P.  per  Cu.  Ft. 

Lbs.  per  H.  P. 

5 

.  6600 

29.852 

10 

-7253 

28.723 

14.7 

•7540 

28.252 

25 

.7879 

27.717 

40 

.8238 

27.170 

60 

.8649 

26-573 

80 

•Q033 

26.038 

100 

.9406 

25-537 

125 

.9865 

24.945 

150 

2.0321 

24-387 

What  is  sometimes  called  the  "boiler-heat  horse-power"* 
is  the  power  corresponding  to  the  energy  imparted  to  the 
steam  by  its  evaporation  within  the  boiler.  This  power  is 
measured  by  dividing  the  weight  of  steam  made  by  that  re- 
quired to  produce  unity  of  power,  and  the  latter  quantity  is 
obtained  by  dividing  the  energy  in  foot-pounds  of  one  horse- 
power per  hour  by  the  mechanical  equivalent  of  the  latent 
heat  of  steam  ;  i.e., 


^  2-65  lbs- 


Taking  as  a  standard  the  quantity  of  steam  demanded  by  a 
perfect  engine,  having  no  clearance,  receiving  steam  at  boiler- 
pressure,  and  expanding  it  down  to  a  perfect  vacuum,  or  to  the 
atmospheric  pressure,  we  may  readily  obtain  figures  for  the 
weights  demanded  by  which  to  rate  steam-boilers,  should  it  be 
found  necessary  to  resort  to  such  an  ideal  system.  For  such 
cases,-  Ze-uner's  f  figures  are  as  below  : 


*  "  Boiler-power  and  Boiler-heating  Surface,"  by  Professor  R.  H.  Smith,  In- 
dustries, July  i,  1887. 
f  War  me  Theorie. 


STEAM  AND  ITS  PROPERTIES. 


295 


WATER  PER  HORSE-POWER  PER  HOUR. 

PRESSURE 
ATMOSPHERES. 

Non-condensing  Engine. 

Condensing  Engine. 

Lbs. 

Kilogs. 

Lbs. 

Kilogs. 

3 

33 

1  51 

13 

6 

4 

26 

12 

12 

51 

5 

23 

io£ 

Hi 

5i 

6 

21 

9* 

II 

5 

8 

18 

8 

10* 

4f 

10 

idi 

7i 

10 

4i 

1 

In  this  case  the  rated  power  of  the  boiler  would  be  obtained 
by  dividing  the  weight  of  steam  made  per  hour  by  the  proper 
figure  from  the  above  table. 

Assuming  the  actual  kinetic  energy  of  the  issuing  steam  to 
measure  the  actual  available  power  of  the  boiler,  we  find  that 
if  the  size  of  the  orifice  is  just  sufficient  to  discharge  the  steam 
as  rapidly  as  it  is  generated,  the  work  done  by  the  boiler  will 
be 


and  the  power 


H.P.  =  --,55* 


or  H.  P.  = 


(2) 


when  w  is  the  weight  of  steam  made,  and  v  its  velocity  of  out- 
flow per  second,  the  one  expression  being  in  British,  the  other 
in  metric  measures. 

Again  taking  Zeuner's  figures,  we  have 


PRESSURE 
ATMOSPHERES. 

3 

4 

5 

6.. 


VELOCITIES  PER  SECOND. 

Metres.        Feet. 

185          607 

208          68l 


10. 


227 

230 

255 
260 


734 
775 
835 
879 


296  THE   STEAM-BOILER. 

and  the  horse-power  actually  delivered  on  this  basis  would  be 
obtained  by  inverting  these  values  in  the  expression  above. 
So  using  them,  we  obtain  for  the  power  of  the  boiler, 


PRESSURE 
ATMOSPHERES. 

H.  P.  =  ^ 

1  1  2W  j 

1407^ 

4. 
c 

1657*!' 

6 

I847C' 

8 

2OI7£' 

10.  . 

2MW 

m 


Ibs.         5i7c/w  in  kilos. 

647C',« 

75WW 
842001 

9 1  7c';« 


The  work  done  by  the  boiler  is  thus  obtained  by  multiply- 
ing the  weight  of  steam  made  per  second  by  the  figures  here 
given. 

This  system  may  be  called  the  natural  system  of  rating 
power.  Where  a  similar  system  is  adopted,  but  the  total  re- 
sistance of  the  atmosphere  is  allowed  for,  as  proposed  by 
Nystrom  for  the  "  legal "  horse-power,  the  quantity  of  heat  and 
of  steam  demanded  is  increased,  at  usual  pressures,  about  one 
half.  Nystrom  proposed  to  assume  a  fixed  rate  of  combustion 
and  proportions  of  parts.  His  method  may  be  illustrated  as 
follows : 

A  cubic  foot  of  water,  when  evaporated,  forms  a  definite 
volume  of  steam  ;  and  if  we  take  the  product  of  the  volume  of 
water  evaporated  per  hour,  the  increase  of  volume  by  its  con- 
version into  steam,  the  pressure  of  the  steam,  and  divide  this 
product  by  1,980,000,  the  quotient,  which  is  the  power  this 
steam  can  develop  in  a  non-condensing  engine,  without  expan- 
sion, is  the  horse-power  of  the  boiler.  Suppose,  for  example, 
that  a  boiler  evaporates  25  cubic  feet  of  water  per  hour,  and 
that  the  pressure  of  the  steam  above  the  atmosphere  is  130  Ibs. 
per  square  inch,  or  18,720  Ibs.  per  square  foot.  The  relative 
volume  of  steam  of  this  pressure  is  192.83,  so  that  the  increase 
of  volume  for  each  cubic  foot  of  water,  on  its  conversion  into 
steam,  is  191.83  cubic  feet,  and  the  horse-power  of  the  boiler  is 
the  product  of  25,191.83,  and  18,720  divided  by  1,980,000,  or 
45-3  +• 


STEAM  AND  ITS  PROPERTIES. 

He  would  take  the  power  of  a  boiler  to  be 


297 


HLfc-.4/S3; 


10 


(2) 


in  which  formula  F  and  5  are  the  areas  of  grate  and  heating 
surface  in  square  feet.  Thus  a  boiler  having  100  square  feet 
of  grate  and  3000  feet  of  heating  surface,  at  75  pounds  pressure 
above  vacuum,  would  rate  at 


H.  P.  = 


X  3000  X  V'7S  =  5IQ. 


which  is  far  above  the  usual  power  of  steam-boilers  with  natural 
draught. 

Small  engines,  according  to  Buel,  demand  steam,  ordinarily, 
as  below : 

FEED-WATER  REQUIRED  BY  SMALL  ENGINES. 


Pressure  of  Steam  in 
Boiler,  by  Gauge. 
10 

Pounds  of  Water  per 
effective  Horse- 
power per  Hour. 
Il8 

Pressure  of  Steam  in 
Boiler,  by  Gauge. 
60 

Pounds  of  Water  per 
effective  Horse- 
power per  Hour. 

75 

15 

III 

70 

71 

20 

105 

80 

68 

25 

100 

90 

65 

30 

93 

100 

63 

40 

84 

120 

61 

50 

79 

ISO 

58 

Pressures  lower  than  60  pounds  are  not  usually  adopted  for 
small  engines.  Good  examples  of  such  engines  have  been 
found  by  the  Author  to  demand  from  25  to  33  per  cent  less 
steam,  or  feed-water,  than  is  above  given. 

The  following  are  considered  by  the  Author  as  fair  estimates 
of  water  and  steam  consumption  for  the  best  classes  of  engines 
in  common  use,  when  of  moderate  size  and  in  good  order : 


2Q8 


THE   STEAM-BOILER. 


WEIGHTS  OF  FEED-WATER  AND   OF  STEAM. 

NON-CONDENSING  ENGINES. 


STEAM  PRESSURE. 

POUNDS  PER  H.  P.  PER  HOUR.  —  RATIO  OF  EXPANSION. 

Atmospheres. 

Lbs.  per 
sq.  in. 

2 

3 

4 

5 

7 

10 

3 

45 

40 

39 

40 

40 

42 

45 

4 

60 

35 

34 

36 

36 

38 

40 

5 

75 

30 

28 

27 

26 

30 

32 

6 

90 

28 

27 

26 

25 

27 

29 

7 

105 

26 

25 

24 

23 

25 

27 

8 

120 

25 

24 

23 

22 

22 

21 

10 

150 

24 

23 

22 

21 

20 

20 

CONDENSING    ENGINES. 


2 

30 

30 

28 

28 

30 

35 

40 

3 

45 

28 

27 

27 

26 

28 

32 

4 

60 

27 

26 

25 

24 

25 

27 

5 

75 

26 

25 

25 

23 

22 

24 

6 

90 

26 

24 

24 

22 

21 

20 

8 

1  20 

25 

23 

23 

22 

21 

2O 

10 

150 

25 

23 

22 

21 

20 

»9 

It  is  considered  usually  advisable  to  assume  a  set  of  practi- 
cally attainable  conditions  in  average  good  practice,  and  to  take 
the  power  so  obtainable  as  the  measure  of  the  power  of  the 
boiler  in  commercial  and  engineering  transactions.  The  unit 
generally  assumed  has  been  usually  the  weight  of  steam  de- 
manded per  horse-power  per  hour  by  a  fairly  good  steam-en- 
gine. This  magnitude  has  been  gradually  decreasing  from  the 
earliest  period  of  the  history  of  the  steam-engine.  In  the  time 
of  Watt,  one  cubic  foot  of  water  per  hour  was  thought  fair;  at 
the  middle  of  the  present  century,  ten  pounds  of  coal  was  a 
usual  figure,  and  five  pounds,  commonly  equivalent  to  about 
forty  pounds  of  feed-water  evaporated,  was  allowed  the  best 
engines.  After  the  introduction  of  the  modern  forms  of  en- 
gine this  last  figure  was  reduced  twenty-five  per  cent,  and  the 
most  recent  improvements  have  still  further  lessened  the  con- 
sumption of  fuel  and  of  steam.  By  general  consent,  the  unit 
has  now  become  thirty  pounds  of  dry  steam  per  horse-power 
per  hour,  which  represents  the  performance  of  good  non-con- 
densing mill-engines.  Large  engines,  with  condensers  and 


STEAM  AND  ITS  PROPERTIES.  299 

compounded  cylinders,  will  do  still  better.  A  committee  of 
the  American  Society  of  Mechanical  Engineers*  recommended 
thirty  pounds  as  the  unit  of  boiler-power,  and  this  is  now  gene- 
rally accepted.  They  advised  that  the  commercial  horse-power 
be  taken  as  an  evaporation  of  yd  pounds  of  water  per  hour  from 
a  feed-water  temperature  of  100°  Fahr.  into  steam  at  70  pounds 
gauge  pressure,  which  may  be  considered  to  be  equal  to  34^ 
units  of  evaporation,  that  is,  to  34^  pounds  of  water  evapo- 
rated from  a  feed-water  temperature  of  212°  Fahr.  into  steam 
at  the  same  temperature.  This  standard  is  equal  to  33,305 
British  thermal  units  per  hour.f 

It  was  the  opinion  of  this  committee  that  a  boiler  rated  at 
any  stated  power  should  be  capable  of  developing  that 
power  with  easy  firing,  moderate  draught,  and  ordinary  fuel, 
while  exhibiting  good  economy,  and  at  least  one  third  more 
than  its  rated  power  to  meet  emergencies. 

Any  increase  of  temperature  derived  from  a  heater  should 
not  be  credited  to  the  efficiency  of  the  boiler  except  by  agree- 
ment ;  and  in  the  latter  case  tests  should  be  made  only  with 
feed-water  of  the  temperature  observed  during  the  regular 
operation  of  the  boiler. 

*  Trans.,  vol.  vi.,  Nov.  1881. 

f  According  to  the  tables  in  Porter's  Treatise  on  the  Richards  Steam-engine 
Indicator,  which  tables  the  committee  adopt,  an  evaporation  of  30  pounds  of  water 
from  100°  F. ,  into  steam  at  70  pounds  pressure,  is  equal  to  an  evaporation  of 
34.488  pounds  from  and  at  212°  ;  and  an  evaporation  of  34^  pounds  from  and  at 
212°  F.  is  equal  to  30.010  pounds  from  100°  F.,  into  steam  at  70  pounds  pressure. 

The  "  unit  of  evaporation"  being  equal  to  965.7  thermal  units,  the  commercial 
horse-power  =  34.488  X  965.7  =  33.305  thermal  units. 


.  CHAPTER   VII. 

THE   DESIGN   OF   THE   STEAM-BOILER. 

146.  The   Design  of  the  Steam-Boiler  is  a  problem  in 
construction  which  involves  vastly  more  than  the  mere  applica- 
tion, of  chemical  and  physical  principles,  and  the  calculation  of 
areas  of  grate  and  heating  surfaces.     The  first  step  in  its  solu- 
tion is  the  study  of  the  conditions  under  which  the  steam  is  to 
be  produced  and  utilized ;  the  location  and  space  available ;  the 
kind  and  cost  of  fuel ;  the  nature  and  availability  of  the  supply 
of  feed-water ;  the  pressure  to  be  adopted ;  the  facilities  to  be 
obtained  for  repairs ;  and  many  other  conditions,  of  which  the 
financial  and  commercial  are  as  important  as  any  others,  must 
all  be  taken  into  careful  consideration. 

The  problem,  stated  in  the  most  general  and  comprehensive 
way,  may  be  said  to  be  the  following : 

Required ' :  To  determine  what  type,  proportions,  size,  and 
construction  of  boiler  may  be  made,  in  the  location  chosen,  and 
under  all  the  natural  and  artificial  conditions  found  there  to 
exist,  to  supply  a  given  amount  of  steam  at  least  total  risk  and 
cost. 

The  business  aspects  of  the  case  must  be  as  conscien- 
tiously studied  by  the  designing  engineer  as  those  of  pure  en- 
gineering. 

The  design  of  the  steam-boiler  is  thus  a  problem  in  en- 
gineering which  demands  careful  consideration,  accurate  knowl- 
edge of  the  principles  controlling  proportions  and  performance, 
and  perfect  familiarity  with  the  conditions  to  be  met  in  the 
case  in  hand. 

147.  The  Choice  of  Type  of  Boiler  and  its  Location  is 
the  first  step  to  be  taken  preparatory  to  commencing  the  de- 
sign.   The  type  best  adapted  for  the  special  case  is  determined 
by  the  conditions  of  location  and  purpose,  as  whether  station- 


THE  DESIGN   OF   THE   STEAM-BOILER.  301 

ary,  portable,  locomotive,  or  marine ;  by  the  pressure  and  quan- 
tity of  steam  demanded ;  by  the  character  of  the  feed-water 
and  fuel,  and  the  cost  of  obtaining  it  ;  by  the  facilities  to  be 
had  for  repairs,  etc. 

Where  the  boiler  is  to  be  used  on  land,  the  standard  loco- 
motive and  stationary  boilers  may  be  used,  if  found  otherwise 
advisable  ;  but  on  shipboard  it  is  essential  that  the  boiler  should 
be  "  self-contained,"  and  the  common  stationary  boilers  cannot 
be  employed.  Each  application  is  best  made,  as  a  rule,  by 
the  employment  of  some  one  of  those  forms  which  have  been 
classed  above,  and  certain  types  are  thus  standard  for  each 
location. 

Among  stationary  boilers  the  plain  cylindrical  is  chosen 
when  the  cost  of  fuel  is  low,  when  the  feed-water  is  bad,  or 
when  the  facilities  for  repairing  are  not  good.  As  the  necessity 
for  economy  in  fuel-consumption  becomes  greater,  and  when 
the  character  of  the  feed-water  is  good,  the  more  complicated 
flue  or  tubular  boilers  are  selected  ;  or  the  dictates  of  prudence 
may  lead  to  the  selection  of  some  one  of  the  so-called  "  safety" 
or  "  sectional  "  boilers,  even  where  cost  and  other  considera- 
tions would  weigh  against  them. 

The  most  common  form  of  stationary  boiler  in  the  United 
States,  in  ordinary  good  locations,  is  the  cylindrical  tubular 
boiler ;  in  Great  Britain  the  Cornish  and  the  Galloway  boilers 
are  much  used  ;  while  on  the  continent  of  Europe  the  "  ele- 
phant" boiler  is  more  common.  In  all  directions,  however,  the 
safer  forms  of  boiler  are  gaining  ground. 

The  "portable"  boiler  is  usually  an  upright  tubular,  with 
firebox  beneath,  for  very  small  powers,  and  a  horizontal  boiler 
of  the  locomotive  type  for  larger  sizes.  It  must  always  be  "  self- 
contained  "  in  the  sense  of  having  no  "  setting,"  and  is  com- 
monly made  the  foundation  or  bed  for  its  attached  engine, 
somewhat  as  in  locomotives. 

The  locomotive  boiler  has  become  fixed  in  type,  and  nearly 
fixed  in  proportions.  All  builders  adopt  the  horizontal,  cylin- 
drical tubular  shell  with  firebox.  Here,  as  in  all  cases  in  which 
high  pressures  are  employed,  cylindrical  or  strongly  stayed  sur- 
faces are  found  essential  to  safety  and  durability.  Many  other 


302  THE   STEAM-BOILER. 

designs  of  boiler  have  been  proposed  and  experimentally  em- 
ployed for  locomotives,  but  none  has  survived. 

The  marine  steam-boiler  is  the  product  of  a  long  process  of 
evolution  which  has  led  to  the  gradual  reduction  of  a  variety 
of  forms  to  a  few  standards.  Thus,  at  sea,  the  "drum"  or 
Scotch  boiler,  described  in  article  19,  has  become  almost  uni- 
versally adopted  where  high  pressures  are  employed,  as  it  is 
stronger,  more  compact,  and  more  economical  than  its  rivals, 
and  is  self-contained. 

The  location  of  a  boiler  is  sometimes  a  matter  of  choice 
with  the  engineer  preparing  the  plans,  and  may  be  one  of 
serious  importance.  Where  possible  it  should  always  be  so 
chosen  that  the  boiler  may  be  easy  of  access  for  inspection  and 
repair ;  it  should  be  free  from  special  danger  to  lives  or  sur- 
rounding property  in  case  of  accident,  and  the  site  selected 
should  be  dry  and  well  protected  against  the  weather.  The 
nearer  the  engine  or  other  point  at  which  its  steam  is  delivered 
the  better.  Only  sectional  boilers  should  be  placed  under 
buildings.  Shell-boilers  should  have  boiler-houses  constructed 
for  them  apart  from  the  larger  and  more  important  structures 
to  which  they  are  auxiliary,  and  this  precaution  is  especially 
advisable  for  cases,  as  mills,  in  which  many  lives  may  be  en- 
dangered. The  risk  involved  is  not  great  where  these  boilers 
are  well  designed  and  constructed ;  but  the  prudent  engineer 
avoids  even  moderate  risk  where  a  life  is  involved. 

When  the  space  is  restricted  in  floor-area,  but  of  good 
height,  the  upright  tubular  boiler  is  selected  ;  if  the  floor-area 
is  unrestricted,  but  head-room  is  small,  the  horizontal  forms  of 
boiler  are  chosen.  Good  forms  of  "  safety "  boilers  may  be 
placed  wherever  they  can  be  given  room,  provided  they  are 
accessible  for  inspection,  cleaning,  and  repairs. 

148.  The  Choice  of  Fuel  and  of  Method  of  Combustion 
is  commonly  necessarily  made  before  the  design  can  be  pro- 
ceeded with.  The  fuel  is,  as  a  rule,  selected  mainly  with  a  view 
to  commercial  efficiency ;  but  the  presence  of  any  observable 
quantity  of  sulphur  in  coal  justifies  its  rejection  at  even  con- 
siderable pecuniary  sacrifice.  That  fuel  is  best  which  produces 
the  required  quantity  of  steam  with  certainty  and  regularity 


THE   DESIGN  OF   THE   STEAM-BOILER.  303 

under  the  given  conditions,  and  at  minimum  total  cost  for 
purchase,  transportation  and  handling,  storage,  interest  and 
insurance,  and  wear  and  tear  of  apparatus.  As  a  rule,  the  least 
costly  fuels  are  most  economical,  if  the  furnace  is  properly 
adapted  to  them  ;  but  it  is  not  always  so,  and  the  user  will 
generally  solve  the  problem  by  experiment  and  experience. 
The  conditions  of  the  market  are  very  apt  to  control,  and 
anthracite  fuel  in  the  Eastern  United  States,  bituminous  coals 
throughout  the  West,  and  wood  in  forested  countries  are 
naturally  the  staple  fuels.  On  the  border  lines,  or  even  within 
either  territory,  prices  may  be  so  adjusted  that  the  question 
may  be  difficult  to  decide  until  after  prolonged  trial  of  two  or 
more  kinds  which  may  be  available.  In  the  case  of  the  "soft" 
coals  the  decision  of  the  question  whether  the  fuel  shall  be 
used  in  its  natural  state,  or  coked,  may  often  demand  con- 
sideration. For  metallurgical  purposes  coke  is  commonly 
used,  but  for  steam-boilers  the  raw  coal  is  most  generally 
adopted. 

The  combustion  may  be  produced  by  either  a  natural 
chimney  draught  or  a  forced  draught,  created  by  a  fan,  a  steam- 
jet,  or  other  artificial  means.  With  very  fine  coal,  or  where  the 
grate-area  or  the  boiler  itself  is  so  small  as  to  make  the  rate 
of  combustion  due  to  natural  draught  insufficient,  the  blast  is 
employed.  The  locomotive  and  the  torpedo-boat  illustrate 
this  case.  A  closed  fire-room,  made  air-tight,  and  into  which 
the  blast  is  driven  and  allowed  to  enter  the  furnace  precisely 
as  with  a  chimney  draught,  is  regarded  by  many  engineers  as 
the  best  method  of  securing  rapid  combustion.  Where  the 
area  of  heating-surface  is  the  same  in  proportion  to  the  amount 
of  coal  burned,  this  system  is  fully  as  economical  as  the  others. 
The  proportion  of  heating  to  grate  surface  being  fixed,  or 
nearly  constant,  as  is  common,  the  slower  combustion,  down  to 
certain  limits  is  naturally  the  more  efficient.  Natural  draught 
is  to  be  preferred  where  the  desired  amount  of  steam  may  be 
made  by  that  system. 

149.  The  Conditions  of  Efficiency  in  steam-boilers  are 
those  affecting  the  production,  the  transfer,  and  the  storage  of 
the  heat-energy  derivable  from  the  fuel.  These  have  already 


304  THE   STEAM-BOILER. 

been  considered.  En  resumt :  the  efficient  production  of  heat 
requires  the  concentrated  combustion  of  the  fuel,  with  the 
minimum  air-supply  consistent  with  the  complete  combination 
of  its  oxidizable  elements  with  oxygen,  and  the  attainment'  of 
maximum  temperature.  The  efficient  transfer  and  storage  in 
the  steam  of  this  heat  demands  that  it  be  liberated  at  maxi- 
mum temperature,  that  the  heating-surfaces  be  of  great  extent 
in  proportion  to  the  weight  of  fuel  burned  and  to  the  quantity 
of  heat  liberated,  and  that  these  surfaces  be  effective  in  absorp- 
tion of  heat.  The  formula  deduced  in  Chapter  IV.  for  effi- 
ciency of  heating-surface  gives  a  measure  of  the  efficiency  of 
the  boiler  when  the  value  of  the  fuel  is  known,  and  includes 
efficiency  of  transfer  and  of  storage. 

150.  The  Principles  of  Design,  in  the  case  of  the  steam- 
boiler,  involve  those  of  strength  of  materials  and  of  structures, 
the  determination  of  the  size,  form,  and  proportions  of  parts  ; 
the  relation  of  area  of  heating  and  of  grate  surface  to  fuel 
burned ;  the  character  and  proportions  of  accessory  parts ;  in 
fact,  the  application  of  all  the  data  and  the  laws  which  have 
been  studied  in  the  preceding  portions  of  this  work.  The  de- 
signing engineer  must  determine  the  form  and  proportions  of 
a  vessel  in  which  is  to  be  generated  a  given  quantity  of  steam 
with  satisfactory  efficiency  and  safety,  and  with  as  nearly  per- 
manent commercial  success  as  possible. 

The  settlement  of  the  general  proportions  of  the  structure 
is  made  with  reference  to  the  above  considerations  ;  but  gen- 
eral experience  has  brought  these  proportions  into  a  fairly 
definite  relation,  and,  as  an  illustration,  the  better  classes  of 
boiler  rarely  have  a  less  ratio  of  heating  to  grate  surface,  where 
natural  draught  is  adopted,  than  about  25  to  i,  or  a  higher 
ratio  than  40  to  I.  With  more  intense  combustion  and  forced 
draught  this  proportion  is  considerably  increased.  The  best 
proportion  is  probably  usually  capable  of  fairly  exact  calcula- 
tion by  a  method  to  be  considered  at  some  length  in  a  later 
chapter.  Boiler-power  is  very  often  calculated,  in  cases  of 
ordinary  practice,  by  allowing  a  certain  number  of  square  feet 
of  heating-surface  to  the  horse-power.  Thus,  the  following 
may  be  taken  as  a  fair  average  set  of  figures : 


THE   DESIGN   OF    THE   STEAM-BOILER.  305 

Plain  cylinder-boiler 8 

Flue-boiler 10 

Water-tube  or  sectional  boiler 12 

Locomotive  boiler  13 

Return  tubular  boiler 15 

Upright  tubular  boiler 1 8 


Careful  calculation   should  be  resorted  to  in  every  impor- 
tant case. 

In  designing  boilers  the  effort  of  the  engineer  should  be — 

(1)  To    secure    complete  combustion  of   the    fuel   without 
permitting  dilution  of  the  products  of  combustion  by  excess 
of  air.     A  combustion-chamber  is  usually  desirable/ 

(2)  To  secure  as  high  temperature  of  furnace  as  possible. 

(3)  To  so  arrange  heating-surfaces  that,  without  checking 
draught,  the  available  heat  shall  be  most  completely  taken  up 
and  utilized  and  the  most  complete  and  rapid  circulation  se- 
cured, both  for  the  water  and  for  the  furnace-gases. 

(4)  To  make   the  form  of  boiler  so  simple  that  it  may  be 
constructed  without  mechanical  difficulty  or  excessive  expense, 
and    to   arrange    for   ample   water-surface,    as   well    as    large 
steam  and  water  capacity,  so  as  to  insure  against  serious  fluc- 
tuation of  steam-supply. 

(5)  To  give  it  such  form  that  it  shall  be  durable,  under  the 
action  of  hot   gases,  and  of  corroding  elements  of  the  atmos- 
phere. 

(6)  To  make  every  part  accessible  for  cleaning  and  repairs. 

(7)  To   make    all    parts   as   nearly  as   possible    uniform    in 
strength,  and  in  liability  to  loss  of  strength  with  age,  so   that 
the  boiler,  when  old,  shall  not  be  rendered  useless  or  dangerous 
by  local  defects. 

(8)  To  adopt  >a  reasonably  high  •*  factor  of  safety"  in  pro- 
portioning parts,  and  to  provide  against  irregular  strains  of  all 
kinds. 

(9)  To    provide  efficient    safety-valves,  steam-gauges,  mud- 
drums,  and  other  appurtenances. 

(10)  To  secure  intelligent  and  very  careful  management. 

In  securing  complete  combustion — the  first  of  these  desiderata 
— an  ample  supply  of  air  and  its  thorough  intermixture  with  the 


306  THE   STEAM-BOILER. 

combustible  elements  of  the  fuel  is  essential ;  for  the  second — 
high  temperature  of  furnace — it  is  necessary  that  the  air-supply 
shall  not  be  in  excess  of  that  absolutely  needed  to  give  com- 
plete combustion.  The  efficiency  of  a  furnace  is  measured  by 

T      T1 
F  —      ~~ 
"T-  7' 

in  which  E  represents  the  ratio  of  heat  utilized  to  the  whole 
calorific  value  of  the  fuel  ;  T  is  the  furnace  temperature  ;  T1 
the  temperature  of  the  chimney,  and  t  that  of  the  external  air. 
Hence  the  higher  the  furnace-temperature  and  the  lower  that 
of  chimney,  the  greater  the  proportion  of  available  heat. 

It  is  further  evident  that,  however  perfect  the  combustion, 
no  heat  can  be  utilized  if  either  the  temperature  of  chimney 
approximates  to  that  of  the  furnace,  or  if  the  temperature  of 
the  furnace  is  reduced  by  dilution  to  that  of  the  chimney. 
Concentration  of  heat  in  the  furnace  is  secured,  in  some  cases, 
by  special  expedients,  as  by  heating  the  entering  air,  or,  as  in 
the  Siemens  gas-furnace,  heating  both  the  combustible  gases 
and  the  supporter  of  combustion.  Detached  fire-brick  fur- 
naces have  an  advantage  over  the  "  fireboxes"  of  steam-boilers 
in  their  higher  temperature  ;  surrounding  the  fire  with  non- 
conducting and  highly  heated  surfaces  is  an  effective  method 
of  securing  high  furnace-temperature. 

In  arranging  heating-surface,  the  effort  should  be  to  impede 
the  draught  as  little  as  possible,  and  so  to  place  them  that  the 
circulation  of  water  within  the  boiler  should  be  free  and  rapid 
at  every  part  reached  by  the  hot  gases. 

The  direction  of  circulation  of  water  on  the  one  side  and  of 
gas  on  the  other  side  the  sheet  should,  whenever  possible,  be 
opposite.  The  cold  water  should  enter  where  the  cooled  gases 
leave,  and  the  steam  should  be  taken  off  farthest  from  that 
point.  The  temperature  of  chimney-gases  has  thus  been  re- 
duced by  actual  experiment  to  less  than  300°  Fahr.,  and  an 
efficiency  equal  to  0.75  to  0.80  the  theoretical  is  attainable. 

The  extent  of  heating-surface  simply,  in  all  of  the  best 
forms  of  boiler,  determines  the  efficiency,  and  the  disposition 


THE   DESIGN  OF   THE   STEAM-BOILER.  307 

of  that  surface  seldom  affects  it  to  any  great  extent.  The 
area  of  heating-surface  may  also  be  varied  within  very  wide 
limits  without  greatly  modifying  efficiency.  A  ratio  of  25  to  I 
in  flue  and  30  to  I  in  tubular  boilers  represents  the  relative  area 
of  heating  and  grate  surfaces  in  the  practice  of  many  of  the 
best-known  builders. 

The  factor  of  safety  is  usually  too  low.  The  boiler  should 
be  built  strong  enough  to  bear  a  pressure  at  least  six  times  the 
proposed  working-pressure.  As  it  grows  weak  with  age,  it 
should  be  occasionally  tested  to  a  pressure  at  least  double  the 
working-pressure,  which  latter  should  be  reduced  gradually  to 
keep  within  the  bounds  of  safety. 

151.  The  Controlling  Ideas  in  designing  dictate  the  follow- 
ing procedure.  The  engineer  determines — 

(1)  The  height  of  chimney,  and  rate  of  combustion  desira- 
ble or  practicable. 

(2)  The  type  of  boiler,  having  regard  to  the  character  of 
water  to  be  used  as  "  feed,"  and  the  costs  of  construction,  opera- 
tion, and  maintenance. 

(3)  The  quantity  of  steam  that  will  be  demanded. 

(4)  The  efficiency  of  boiler  that  it  will  be  economical  to  se- 
cure, according  to  the  principles  to  be  given,  and  thus  the  ratio 
of  heating  to  grate  surfaces. 

(5)  The  kind  and  the  quantity  of  fuel  required,  with  the 
given   or  proposed  efficiency,  to  produce  the  demanded  quan- 
tity of  steam. 

(6)  The  total  areas  of  grate  and  of  heating  surface  required 
to  burn  that  fuel  and  to  make  that  steam. 

(7)  The  forms,  sizes,  and  proportions  of  details. 

The  dimensions  and  proportions  of  the  boiler  plant  being 
thus  determined,  the  engineer  decides  what  amount  of  power 
shall  be  obtained  from  a  single  boiler,  and  thus  how  many  boil- 
ers are  to  be  constructed,  the  area  of  heating  and  grate  surface 
to  be  given  each  ;  and  he  finally  decides  upon  the  form  of  set- 
ting, and  method  of  making  steam  and  water  connections. 

It  then  remains  only  to  make  a  drawing  of  the  boiler, 
which  shall  show  its  form  and  dimensions,  the  arrangement  of 


308  THE   STEAM-BOILER. 

stays,  pipes,  safety,  and  other  attachments,  and  the  setting. 
The  first  plan  constructed  will  usually  require  some  modifica- 
tion to  adapt  it  exactly  and  satisfactorily  to  the  wants  of  the 
user;  which  changes  being  made,  the  boiler  may  be  constructed 
from  the  drawing.  The  thickness  of  shell,  size  of  tubes  or  flues, 
sizes,  methods,  and  distribution  of  stays,  and  similar  matters  of 
detail,  are  settled  by  well-known  rules  of  practice,  or  by  the 
consideration  of  the  peculiar  conditions  met  with  in  the  case  in 
hand. 

Especial  care  should  be  taken  to  give  all  parts  ample  strength, 
with  a  fair  and  safe  allowance  for  corrosion  ;  to  see  that  every 
part  is  easily  accessible  for  inspection  and  repair;  that  all  de- 
tails are  of  good  form  and  proportions ;  and  that  all  accessories 
and  attachments  are  the  best  and  safest  of  their  kind. 

The  Steam-pressure  to  be  adopted  will  necessarily  be  one  of 
the  first  matters  to  be  considered  and  settled  ;  both  because  it 
has  an  important  bearing  upon  the  efficiency  of  the  engine  and 
because  it  must  be  kept  in  view  in  the  selection  of  the  type 
and  size  of  boiler.  The  tendency  is  constantly  in  the  direction 
of  higher  steam-pressure,  and  the  consequent  adoption  of  the 
simpler,  stronger,  and  safer  kinds  of  boiler.  This  directly  con- 
flicts with  the  commercial  considerations  affecting  boiler-con- 
struction, especially  of  the  common  forms  of  shell-boiler.  The 
larger  the  boiler,  as  a  rule,  the  cheaper,  comparatively,  its  con- 
struction, the  less  the  cost  of  setting  and  of  installation,  and 
the  higher  its  economy  in  operation.  A  large  shell,  however, 
must  be  made  of  thicker  iron,  and  is  always  somewhat  less  ab- 
solutely safe  than  a  similar  smaller  structure. 

A  limit  is  thus  being  continually  approached  because  of  the 
fact  that  the  net  gain  is  less  and  less  as  the  increase  occurs  at 
higher  pressures.  An  increase  from  100  to  200  pounds  may 
give  a  calculated  gain  of  12  or  15  percent;  but  the  net  gain 
will  be  actually  much  less,  and  may  not  be  enough  to  compen- 
sate the  increased  costs  and  risks.  At  the  present  day,  pres- 
sures of  125  to  150  pounds  are  not  unusual ;  but  many  engineers 
consider  it  inadvisable  to  go  much  farther  in  the  direction 
of  increasing  pressure,  and  the  tendency  of  modern  practice  is 


THE  DESIGN  OF    THE   STEAM-BOILER. 


309 


to  restrict  the  adoption  of  such  higher  pressures  to  the  cases  in 
which  the  sectional  types  of  boiler  are  used. 

As  illustrating  the  general  effect  of  increasing  pressures,  and 
the  progressive  diminution  of  the  rate  of  gain,  Mr.  H.  F. 
Smith  has  given  the  following  tables  of  weight  of  steam  and 
coal  demanded*  per  hour  and  per  horse-power,  by  a  perfect 
steam-engine,  Calculated  on  the  assumption  that  1 100  thermal 
units  per  pound  of  coal  are  utilized  by  the  boiler,  which  corre- 
sponds to  an  evaporation  of  about  iiy4^  parts  by  weight  of 
water  from  and  at  the  boiling-point,  per  one  part  of  coal — a  re- 
sult attainable  with  good  coal : 


STEAM  AND  FUEL  CONSUMPTION  IN  A  PERFECT  STEAM-ENGINE. 


STEAM. 

COAL. 

BOILER 

Per  I.  H.  P.  per  hour. 

Per  I.  H.  P.  per  hour. 

PRESSURE. 

TEMPERATURE. 

Per  Gauge. 

Non-con- 

Con- 

Non-con- 

Con- 

densing. 

densing. 

densing. 

densing. 

Lbs.     Atmos. 

Fahr.     Cent. 

Lbs.       Kil. 

Lbs.       Kil. 

Lbs.    Kil. 

Lbs.    Kil. 

300             20 

421.7    216.5 

10.48        4.8 

6.16        2.7 

0.98      .44 

.64      .29 

250        i6§ 

405.9    207.7 

11.19        5-i 

6.39        2.9 

•04       -45 

.66       .30 

200            13^ 

387.6     197  5 

12.  16        5.5 

6.68        3.0 

•13       -Si 

.69       .31 

175     "§ 

377.1     191.7 

12.  81        5.7 

6.87        3  * 

.18       .54 

.71       .32 

150        10 

365.6     185.3 

13.63        6.2 

7.09        3.2 

-25       -57 

•73       -33 

125          8£ 

352  6     167.0 

14.71        6.7 

7-37        3-8 

•35       -6o 

•75       -34 

100          6§ 

337-6     J59-8 

16.24        7-4 

7-71         3-5 

.48       .67 

•78       -35 

90          6 

330.9     166.1 

I7-05         7-7 

7.89        3.6 

•55       -7° 

.80       .36 

80          5% 

323.6     162.0 

18.03        8.2 

8.09         3.7 

•64       -75 

•82       .37 

75          5 

319.8     159.9 

18.60        8.5 

8.19        3.7 

.69       .77 

.83       -38 

7°           4§ 

3*5-7     W-6 

19.25        8.7 

8.32         3-8 

•75       -80 

.84       .39 

60           4 

307.1     152.8 

20.83        9.5 

8-59         3-9 

.88       .85 

•87       -39 

50              33 

297-5     M7-5 

22.95       10.4 

8.92         4.1 

.07       .90 

.90       .40 

45           3 

292.2     144.5 

24-53       "-1 

9.11         4  i 

.19     i.  oo 

.91       .40 

The  table  shows  that  at  high  pressures  the  gain  of  economy  is 
very  slow,  and  that  the  very  best  modern  engines  waste  a  large 
part  of  the  steam  passing  through  the  cylinder.  At  125  pounds, 
if  there  were  no  losses,  three  fourths  of  a  pound  of  coal  per  hour 
would  furnish  one  indicated  horse-power ,  but  very  few  engine- 
builders  can  be  found  who  are  willing  to  guarantee  an  indicated 


3io 


THE   STEAM-BOILER. 


horse-power  with  less  than  one  and  three  fourths  of  a  pound  of 
coal  per  hour  under  the  best  of  conditions. 

A  pound  of  coal,  if  all  the  heat  were  utilized,  would  evapo- 
rate 15  pounds  of  water  from  and  at  the  boiling-point.  Many 
boilers  actually  evaporate  1 1 \  pounds  of  water  with  an  effi- 
ciency of  75  per  cent. 

An  engine  working  perfectly  would  develop  one  indicated 
horse-power  with  7f  pounds  of  steam  (of  125  pounds  initial 
pressure)  per  hour ;  the  best  actual  engines  consume  more  than 
double  this  quantity. 

Mr.  G.  H.  Barrus  gives  the  following  as  the  probable  actual 
steam-consumption  of  good  engines  :* 

FEED-WATER  CONSUMPTION   FOR   NON-CONDENSING  ENGINES. 


Initial 
pressure 
above 
atmosphere. 
Lbs. 

Mean  effective 
pressure. 
Lbs. 

Feed-water 
consumed  per 
I.  H.  P. 
per  hour. 
Lbs. 

Initial 
pressure 
above 
atmosphere. 
Lbs. 

Mean  effective 
pressure. 
Lbs. 

Feed-water 
consumed  per 
I.  H.  P. 
per  hour. 
Lbs. 

AT  10  PER  CENT  CUT-OFF. 

AT  30  PER  CENT  CUT-OFF. 

40 

5° 
60 
70 
80 
90 

IOO 

1.32 
5.01 
8.70 
12.39 
16.07 
19.76 
23-45 

153-24 
52-52 
37.26 

30-99 
27.61 

25-43 
23.90 

40 
50 
60 

7° 
80 
90 

IOO 

16.95 
23-71 
30-47 
37  21 
43-97 
50-73 
57-49 

33-52 
29-35 
27.24 
25-76 
24.71 
23.91 
23.27 

AT  20  PER  CENT  CUT-OFF. 

AT  40  PER  CENT  CUT-OFF. 

40 
50 
60 
70 
80 
90 

IOO 

IO.  22 
IS-G? 
21  .  12 
26.57 
32.O2 

37-47 
42.92 

38.13 
30.98 
27-55 
25-44 
24.04 
23.00 
22.25 

40 

5° 
60 
70 
80 
90 

IOO 

22.24 
29.99 
*7-75 
45-50 
53-25 
61.01 
68.76 

32.79 

29.72 
27.92 
26.26 
25.76 
25.03 
24.47 

AT  50  PER  CENT  CUT-OFF. 


40 

26.40 

33-i6 

80 

60.44 

26.99 

50 

34.91 

3°-53 

90 

68.96 

26.32 

60 

43-42 

28.94 

IOO 

77.48 

25.78 

70 

51-94 

27.79 

*  The  Tabor  Indicator. 


THE   DESIGN  OF   THE   STEAM-BOILER.  311 

FEED-WATER   CONSUMPTION   FOR  CONDENSING  ENGINES. 


Initial 

Feed-water 

Initial 

Feed-water 

pressure 
above 
atmosphere. 
Lbs. 

Mean  effective 
pressure. 
Lbs. 

consumed  per 
I.  H.  P. 
per  hour. 
Lbs. 

pressure 
above 
atmosphere. 
Lbs. 

Mean  effective 
pressure. 
Lbs. 

consumed  per 
I.  H.  P. 
per  hour. 
Lbs. 

AT  5  PER  CENT  CUT-OFF. 

AT  20  PER  CENT  CUT-OFE. 

40 

9-34 

18.99 

40 

23-83 

19.00 

50 

11.88 

18.51 

5° 

29.28 

18.74 

60 

14.42 

18.22 

60 

34-73 

18.98 

70 

16.96 

17.96 

70 

40.18 

18.40 

80 

19.50 

17.76 

80 

45-63 

18.27 

90 

22.04 

17  .  57 

90 

51.08 

18.14 

100 

24.58 

17.41 

100 

56.53 

18.02 

AT  10  PER  CENT  CUT-OFF. 

AT  30  PER  CENT  CUT-OFF. 

40 

14.96 

18.25 

40 

30.54 

20.57 

50 

18.65 

17.91 

50 

37-3° 

20.35 

60 

22.34 

17.68 

60 

44.06 

20.19 

70 

26.03 

17-47 

70 

50.81 

20.04 

80 

29  72 

I7-3° 

80 

57-57 

19.91 

90 

33  4i 

17-15 

90 

64.32 

19.78 

100 

37  -!0 

17.02 

IOO 

71.08 

19.67 

AT  15  PER  CENT  CUT-OFF. 

AT  40  PER  CENT  CUT-OFF. 

40 

19.72 

I8.4I 

4° 

3^.84 

21.94 

50 

24.36 

i8.ii 

50 

43-59 

21.76 

60 

29.00 

17-93 

60 

51.35 

21  .63 

70 

33-65 

70 

59  -I0 

21.49 

80 

38.28 

17.60 

80 

66.85 

21.36 

90 

42.92 

17.45 

90 

74.60 

21  .24 

100 

17-32 

100 

82.36 

21.13 

152.  Safety  and  Efficiency  vs.  Cost  may  be  taken  as  the 
most  serious  part  of  the  problem  to  the  designer  and  user  of 
steam-boilers.  The  safety  of  the  boiler  being  a  first  considera- 
tion, it  becomes  at  once  a  question  how  far  the  engineer  is  justi- 
fied in  sacrificing  money  and  special  advantages  to  secure  safety, 
and  how  closely  he  may  be  practically  able  to  approximate  ab- 
solute security.  To  increase  strength  of  structure  or  of  parts 
means  to  enlarge  the  dimensions,  and  to  thus  increase  expense  ; 
to  select  a  specially  safe  type,  or  peculiarly  safe  construction, 
is  usually  to  meet  the  same  objection ;  and  it  is  soon  found 
that  there  is  a  certain  golden  mean  between  maximum  safety 
and  impracticable  expense  which  gives  most  satisfactory  re- 
sults. For  ordinary  cases,  this  is  probably  found  not  far  from 
those  proportions  which  give  a  "  factor  of  safety"  of  about  six 
for  the  important  parts  of  the  boiler,  although  good  authori- 


312  THE   STEAM-BOILER. 

ties  advise  eight,  and  even  ten,  and  general  practice  often  falls 
to  less  than  four. 

The  same  difficulty  arises  when  it  is  attempted  to  attain 
high  efficiency.  This  must  be  done  by  extension  of  heating- 
surface  and  correspondingly  increased  first  cost  ;  and  it  is 
readily  shown,  as  in  Chapter  XIII.,  that  business  considera- 
tions fix  the  limit  of  efficiency  to  be  sought.  This  efficiency 
being  given,  the  size  and  proportions  of  boiler  become  at  once 
determinable.  Thus  accepting  Rankine's  formula  for  effici- 
ency. already  given  in  article  98,  and  taking  the  desired 
efficiency  as  given  by  calculation  as  E,  the  ratio  of  heating-sur- 

face divided  by  fuel  burned,  —  -  =  R,  will  be  obtained  thus  : 

wj 


........  <* 

Taking  as  common  values  E  =  0.70,  A  =  0.5,  B  •=  i, 

*-%-'?-?  ••-.-•« 

and  the  ratio  of  heating  to  grate-surface  would  be  S  =  --  ;  if 

o.So 

F—  15,  5  =  17.5.     Taking  a  rather  high  efficiency,  E  —  0.80, 
R  —  0.5,  and  5—  30. 

153.  Water-tubes  and  Fire-tubes  have,  respectively, 
their  own  special  advantages  and  disadvantages,  and  these 
differ  in  their  importance  in  different  types  of  boiler.  It  was 
shown  by  experiments  directed  by  Engineer-in-chief  B.  F. 
Isherwood  of  the  U.  S.  Navy,*  that  the  water-tube  boiler  as 
constructed  for  marine  purposes  with  vertical  tubes  is  some- 
what more  economical  than  the  horizontal  fire-tube  boiler  of 
otherwise  similar  type,  and  the  former  excels  in  the  perfection 
of  its  circulation  and  the  readiness  with  which  it  can  be  freed 
from  incrustation  ;  it,  however,  makes  a  heavier  boiler,  and  the 

*  Experimental  Researches  in  Steam  Engineering. 


THE  DESIGN  OF   THE   STEAM-BOILER.  313 

water-tube  is  less  easily  plugged  if  leaking.  This  latter  diffi- 
culty, and  the  inconveniences  and  dangers  arising  from  the 
accumulation  of  salt  in  marine  boilers  when  water  from  in- 
jured tubes  evaporates  in  the  tube-box,  have  caused  the 
disuse  of  this  class  of  boilers.  The  "  sectional  "  class  of  water- 
tube  boilers  is  less  subject  to  such  objections. 

Water-tubes  are  always  set  either  vertical  or  steeply  inclined, 
as  horizontal  or  nearly  horizontal  water-tubes  are  liable  to 
rapid  destruction,  and  are  comparatively  inefficient  because 
of  the  defective  circulation  invariably  distinguishing  them. 
The  fire-tube  may  be  used  in  any  position,  but  is  usually 
placed  horizontally. 

The  general  experience  of  engineers  has  been  such  as  to 
lead  them  to  adopt  the  water-tube  in  the  so-called  "  safety" 
class  of  boilers  and  the  fire-tube  in  others.  The  water-tube  is 
usually  placed  at  an  angle,  in  these  boilers,  of  about  thirty  de- 
grees with  the  horizontal.  In  the  "  Field  tube"  the  position 
is  vertical,  or  nearly  so ;  the  lower  end  is  closed,  and  an  in- 
ternal "  circulating  tube"  permits  the  descent  of  a  solid  column 
of  water  while  the  mingled  steam  and  water  currents  gene- 
rated by  the  heat  applied  to  the  exterior  of  the  main  tube 
rise  unobstructed  to  the  surface. 

Messrs.  Porter  and  Allen  found  that  water-tubes,  closed  at 
the  bottom  and  set  at  an  angle  of  about  thirty  degrees  with 
the  vertical,  were  capable  of  doing  good  work,  and  had  a 
sufficiently  good  circulation  to  give  extraordinarily  high  evapo- 
rative power.  In  all  standard  forms  of  "  shell-boilers"  the 
water-tubes  are  placed  vertically,  and  are  grouped  in  a  low, 
long,  and  usually  narrow  tube-box,  several  of  which  tube-boxes 
are  placed  side  by  side  in  large  boilers. 

The  fire-tube  stands  vertically  in  the  common  "  upright" 
boiler,  and  is  set  horizontally,  as  has  been  seen  in  Chapter  L, 
in  all  the  other  common  forms. 

As  constructed  by  the  best-known  builders,  the  water-tube 
is  expected  to  do  about  twenty  per  cent  more  work  than  the 
fire-tube  of  equal  area.  The  water-tube  shell-boiler  is  in  some 
respects  safer  than  the  fire-tube  boiler;  since  the  water  level 
can  be  carried  below,  and  often  a  considerable  distance  below, 


$14  THE   STEAM-BOILER. 

the  top  of  the  tube  without  endangering  it.     Low  water  with 
the  horizontal  fire-tube  is  always  dangerous. 

154.  Shell  and  Sectional    Boilers,  compared  in  other  re- 
spects than  in  reference  to  safety,  in  which  attributes  the  latter 
are    specially   constructed  to   excel,   are  found,  when   equally 
well  designed  and  constructed,  and  equally  well  managed,  to 
stand  on  substantially  the  same  level. 

The  two  types  of  boiler  in  most  common  use  are  the  water- 
tube  sectional  and  the  cylindrical  fire-tube  (shell)  boiler.  The 
latter  is  in  the  more  extensive  use,  its  cost,  as  a  rule,  being 
less,  its  regularity  of  steam-supply  and  uniformity  of  water- 
level  greater,  while  its  unity  of  structure,  its  convenience  of 
access  for  inspection  and  repair,  and  perhaps  more  than  all, 
the  fact  of  its  having  a  longer  history,  and  being  the  product 
of  a  kind  of  survival  of  the  fittest  of  the  older  types,  giving  it 
a  hold  upon  the  market  that  later  forms  of  boiler  have  not 
secured.  The  former  of  these  two  classes  has  the  grand  ad- 
vantage of  safety  against  disruptive  disastrous  explosions,  has 
equally  good  or  better  circulation  and  general  efficiency,  less 
weight  and  volume  for  equal  powers,  and  greater  reliability  in 
its  details  of  structure.  Its  joints  are  an  objection,  and  its 
usually  less  steady  operation  is  a  disadvantage ;  but  it  is 
rapidly  coming  into  favor  among  engineers,  and  into  use  as 
well. 

The  Author  would  often  use  the  shell-boiler  where  commer- 
cial reasons  would  dictate  such  use,  and,  wherever  practicable, 
would  select  the  externally  fired  cylindrical  fire-tube  boiler,, 
but  would  never  place  a  shell-boiler  under  a  building  in  which 
its  explosion  would  endanger  life  or  much  property :  the 
"  safety"  class  of  boiler  \vould  be  the  only  form  to  be  wisely 
adopted  in  such  locations.  Shell-boilers  should  usually  be 
placed  in  detached  boiler-houses,  and  so  set,  as  to  position,  that 
danger  shall  be  made  a  minimum,  i.e.,  never  pointing  toward 
other  buildings. 

155.  Natural  and  Forced  Draught  both  have  their  advan- 
tages and    their  disadvantages.      Chimney  draught,    unaided, 
gives  a  good  supply  of  air  to  the  fire,  such  as  answers  the  pur- 
pose  well    for  all  ordinary  work  ;  is  free  from  the  objections 


THE  DESIGN  OF   THE   STEAM-BOILER.  315 

introduced  with  all  machinery,  and  especially  those  arising  from 
uncertainty  of  absolutely  reliable  continuous  operation,  and  an 
equally  certain  expense  for  wear  and  tear.  For  the  intense 
draught  and  large  air-supply  needed  when  a  large  amount  of 
fuel  is  to  be  burned  on  a  small  area  of  grate,  the  size  and 
especially  the  height  of  chimney  required,  and  its  cost,  become 
serious  matters,  and  for  such  cases  a  forced  draught  is  the  only 
suitable  system. 

There  are  two  principal  systems  of  forced  draught,  as  al- 
ready noted  :  that  in  which  the  air  is  forced  directly  into  the 
ashpits  through  conduits  leading  from  the  fan  or  other  source 
of  the  blast ;  and  that  in  which  the  current  is  driven  into  the 
fire-room,  or  "  stoke-hole,"  which  is  made  air-tight  for  this  pur- 
pose, and  thence  finds  its  way  to  the  furnaces  precisely  as  when 
a  natural  draught  is  adopted.  Of  these  the  first  is  the  older 
and  more  common  method ;  while  the  second  is  coming  into 
use,  particularly  on  torpedo-boats  and  elsewhere  where  enor- 
mously high  rates  of  combustion  are  to  be  attained  and  kept  up. 
By  the  older  system  the  change  from  the  forced  to  the  natural 
draught  is  very  conveniently  made ;  but  there  is  more  difficulty 
in  handling  the  fires,  and  the  blowing  of  dust  out  into  the 
room,  and  the  danger  of  melting  down  the  grate-bars,  are  two 
decided  disadvantages,  which  are  not  inherent  with  the  system 
involving  the  adoption  of  the  air-tight  fire-room.  In  the  latter 
case  the  fires  are  as  conveniently  and  nearly  as  comfortably 
managed  as  with  natural  draught ;  and  as  all  air  passes  to  the 
furnaces  through  the  fire-room,  if  it  is  well  directed,  the  ventila- 
tion and  cooling  of  the  room  and  the  comfort  of  the  men  are 
comparatively  well  insured. 

A  later  and  in  some  respects  most  satisfactory  system  is 
that  in  which  the  air  is  drawn  into  the  boiler-room  by  a  fan 
placed  as  near  the  furnace  as  possible,  r,nd  then  forced  through 
ducts  into  the  ashpit,  and  into  the  interior  of  hollow  furnace- 
doors  in  such  manner  as  to  intercept  any  gas  that  would  other- 
wise be  liable  to  find  its  way  outward  at  the  furnace  mouth. 

The  Power  required  for  Forced  Draught  is  easily  calculated 
thus: 


316  THE  STEAM-BOILER. 

Let/  =  pressure  of  blast  per  square  foot  ; 
w  —  weight  of  fuel  burned  per  minute; 
F0  =  volume  of  air  per  pound  of  fuel,  at  melting-point 

of  ice  ; 

Ta  =  temperature,  absolute,  at  o°  Fahr.; 
T=  "  "          of  entering  air; 

C  =  coefficient  of  efficiency  of  blast  apparatus. 
Then  the  horse-power  demanded  will  be 


H.P.= 


Thus  for  100  square  feet  of  grate,  at  60  pounds  burned  per 
hour  or  one  pound  per  minute,  per  square  foot,  200  cubic  feet 
of  air  at  32°  F.  per  pound  of  fuel,  when  T0  =493.2,  T  =  532.2, 
C  —  i,/  =  3  inches  of  water  =  16  pounds  per  square  foot. 

16  X  200  X  i  X  532.2 

H.  P.  = ~ —  =  20  nearly. 

33,ocx)  X  493-2  X  i 

But  good  engines  with  such  boilers  should  develop  2000 
horse-power.  The  cost  of  blast  would  thus  be  about  one  per 
cent  of  the  total  power;  while  with  natural  draught  the  cost 
would  probably  be  in  vastly  greater  proportion  in  the  form  of 
waste  heat. 

An  efficient  water-circulation  is  very  important,  and  the 
best  boiler,  as  already  stated,  the  most  efficient  as  well  as  the 
safest,  is  that  in  which,  other  things  being  equal,  the  circulation 
is  most  complete,  general,  rapid,  and  steady.  In  nearly  all 
boilers  the  circulation  is  a  "  natural  "  one  ;  but  occasionally,  as 
in  Pierce's  rotary  boiler,*  as  tested  by  the  Author,  and  later 
at  the  U.  S.  Centennial  Exhibition  of  1876,  and  in  the  boiler 
of  Professor  Trowbridge,  the  circulation  is  a  "  forced  "  one. 
The  last-named  engineer  made  experiments,f  assisted  by  Messrs. 
T.  W.  Mather  and  J.  F.  Klein,  graduate  students  of  the  Shef- 

*  Reports  on  Steam-boilers  at  the  U.  S.  Centennial  Exhibition,  18760 
f  Heat  and  Steam-engines,  p.  146. 


THE  DESIGN  OF   THE   STEAM-BOILER.  317 

field  Scientific  School,  to  determine  the  efficiency  of  forced 
circulation.  The  difficulty  of  constructing  very  small  steam- 
generators  having  sufficient  strength  to  resist  great  pressure, 
and  at  the  same  time  a  high  rate  of  evaporation  with  reason- 
able economy,  has  long  been  recognized.  On  account  of  this 
difficulty  the  use  of  very  small  engines  is  limited.  The  boiler 
in  such  engines  must  have  such  large  proportions  relatively  to 
the  engine  that  it  ceases  to  be  an  economical  apparatus. 

The  object  of  these  experiments  was  to  reduce  the  heating- 
surface,  and  at  the  same  time  make  it  more  efficient  by  a 
forced  and  continuous  circulation  of  the  water  in  the  boiler, 
through  the  means  of  a  circulating  pump.  Various  combina- 
tions and  modes  of  circulation  were  tried,  with  results  which 
appear  conclusive.  A  steam-generator  of  very  small  volume 
and  weight,  made  of  coils  of  gas-pipe,  and  consequently  having 
a  resistance  of  several  thousand  pounds  per  square  inch,  was 
made  to  evaporate  quantities  of  steam  per  hour  which  by  ordi- 
nary processes  would  require  a  boiler  c-f  very  much  greater 
volume.  The  principle  of  forced  circulation  has  not  often  been 
employed  for  this  purpose,  but  there  is  reason  to  believe  that  it 
may  become  practically  useful. 

156.  Special   Conditions  affecting   Design  thus  arise  in 
many  cases,  and  may  absolutely  dictate  the  form  of  the  boiler 
chosen  and  the  place  and  method  of  its  location   and   setting. 
Financial  considerations  often  control ;   the   matter  of  safety 
should  always  be  kept  in  view,  and  may  often  be  the  deciding 
element  in  the  problem.     Peculiarities  of   location  may,   and 
often  do,  determine  the  size   and  form  of   the  boiler  to    be 
chosen,  and  even  the  character  of  the  feed-water  will  frequently 
decide  such  choice.     No  design  is  satisfactory  except  it  meets 
in  the  most  satisfactory  manner  piacticable  every  element  going 
to  make  up  the  whole  problem,  and  is  at  the  same  time  suitable 
for  the  location,  the  specific  work  to   be   done,  and  properly 
meets  the  pecuniary  interests  of  those  concerned,  as  well  as 
gives  the  safest  and  most  efficient  arrangement  possible  under 
the  circumstances. 

157.  The  Chimney  Draught,   and   the   size,   height,  and 
general  construction  of  chimney  and  flues,  are  among  the  first 


318  THE   STEAM-BOILER. 

of  the  details  to  be  settled  when  preparing  to  design  a  steam- 
boiler. 

The  chimney  draught  is  the  first  condition  to  be  studied, 
since  upon  it  primarily  depends  the  power  and  performance 
of  the  boiler.  The  intensity  of  the  draught  in  a  well-propor- 
tioned chimney  will  vary  nearly  as  the  square  root  of  its  height. 
The  quantity  of  fuel  burned  on  the  unit-area  of  grate  is  thus 
determined,  assuming  the  chimney  section  properly  propor- 
tioned to  the  work.  The  sectional  area  of  the  chimney-flue 
should  be  carefully  proportioned  to  the  maximum  weight  of 
fuel  to  be  burned  in  the  unit  of  time. 

Chimneys  are  required  to  carry  off  obnoxious  gases,  and  to 
produce  a  draught.  Each  pound  of  coal  burned  commonly 
yields  from  15  to  50  pounds  of  gas,  the  volume  of  which  varies 
directly  as  the  absolute  temperature. 

The  weight  of  gas  carried  off  by  a  chimney  in  a  given  time 
depends  upon  size  of  chimney,  velocity  of  flow,  and  density  of 
gas.  But  as  the  density  decreases  directly  as  the  absolute 
temperature,  while  the  velocity  increases,  with  a  given  height, 
nearly  as  the  square  root  of  the  temperature,  there  is  a  tem- 
perature at  which  the  weight  of  gas  delivered  is  a  maximum. 
This  is  about  twice  the  absolute  temperature,  or  550°  above, 
•the  surrounding  air.  At  550°  the  quantity  is  only  four  per 
cent  greater  than  at  300°  above  the  ordinary  temperature. 
Height  and  area  are  practically  the  only  elements  necessary 
to  consider  in  an  ordinary  chimney. 

The  intensity  of  draught  is  independent  of  size,  and  varies 
directly  with  the  product  of  the  height  into  the  difference  of 
temperature. 

The  intensity  of  draught  needed  varies  with  the  kind  of 
fuel  and  the  rate  of  combustion  desired,  being  least  for  wood 
and  other  free-burning  fuels,  and  greatest  for  the  finer  coals 
and  "  slack"  or  "brees,"  the  latter  requiring  a  chimney  one 
hundred  and  fifty  to  two  hundred  feet  high,  and  a  difference  of 
pressure  measured  by  an  inch  or  more  of  water. 

The  volume  and  weight  of  gas  discharged  from  any  furnace 
may  be  calculated  as  if  it  were  of  the  density  of  air  at  the  same 
temperature,  the  volume  being  12^  cubic  feet  per  pound,  nearly, 


THE  DESIGN  OF   THE   STEAM-BOILER. 


319 


or  about  three  fourths  of  a  kilogram  to  the  cubic  metre. 
Adopting  British  measures,  if  Fbe  the  volume  per  pound  at 
T,  absolute,  Fahrenheit  degrees, 


V—  Fl 


and  we  obtain,  allowing,  respectively,  12,  18,  or  24  pounds  to 
be  equal  to  150,  225,  and  300  cubic  feet,  the  following  volumes 
of  gases  as  originally  calculated  by  Rankine : 

VOLUMES  OF  GAS  PER  POUND  OF  FUEL  IN  CUBIC 
FEET.  (RANKINE.) 


T 

AIR-SUPPLY  IN  POUNDS  PER  POUND  OF  FUEL. 

12 

18 

24 

4640° 

1551 

32750 

1136 

1704 

.  . 

2500° 

906 

1359 

1812 

1832° 

697 

1046 

1395 

1472° 

588 

882 

1176 

1112° 

479 

718 

957 

752° 

369 

553 

738 

572° 

314 

47i 

628 

392° 

259 

389 

519 

212 

205 

307 

409 

104° 

172 

258 

344 

68° 

161 

241 

322 

32° 

150 

225 

300 

If  w  denotes  the  weight  of  fuel  burned  in  a  given  furnace 
per  second ; 

VQ,  the  volume  at  32°  of  the  air  supplied  per  pound  of  fuel ; 

71,,  the  absolute  temperature  of  the  gas  discharged  by  the 
chimney; 

A,  the  sectional  area  of  the  chimney;  then  the  velocity  of 
the  current  in  the  chimney  in  feet  per  second  is 


u  -  — °^- 


(2) 


and  the  density  of  that  current,  in  pounds  to  the  cubic  foot,  is 
very  nearly  as  in  (3). 


32O  THE   STEAM-BOILER. 

Since  one  cubic  foot  of  air  at  the  temperature  T0  weighs 
about  0.080;  pound,  and  the  weight,  on  the  assumption  of 
uniform  mean  density  of  air  and  gases,  is,  at  J"0,  0.0807  F0-(-i, 
and  its  mean  density  is 


.and  at  r. 

(3) 


Multiplying  D  by  the  height  of  chimney,  //,  the  weight  of 
the  column  per  unit  section  of  its  area,  or,  as  here  taken,  in 
pounds  on  the  square  foot,  becomes 


or,  expressed  in  inches  of  water, 


/  =  O.i9/  ==  0.19^(0.080;  +  Y)>   •     •     •     (5) 

The  loss  of  head,  as  found  by  Peclet,*  may  be  expressed  by 
the  equation 


in  which  /  is  the  total  length  of  flue  from  boiler  to  chimney- 
top,  m  its  hydraulic  mean  depth,  or  area  divided  by  perimeter, 
and  v  the  velocity  of  flow  in  feet  per  second.  When  this  head, 
h',  is  given  we  obtain 

~y& .  L 


13 


*  Trait6  de  la  Chaleur,  vol.  i. 


THE  DESIGN   OF    THE   STEAM-BOILER.  321 

and  the  weight  of  gas  discharged  must  be 

vA       T 


7*!  being  the  temperature  of  flue. 

The  head,  /z,  producing  flow  is  obviously  the  difference  be- 
tween the  weight  of  chimney  gases  and  that  of  the  column  of 
air  of  equal  height  outside  ;  or,  if  Tt  is  the  temperature  of  the 
latter, 


0.0807+- 

* 


H  =   h   -r-   (0.96^-    -   l)  ......    (10) 

The  velocity  of  flow  is  measured  by  a  Vh,  a  being  a  con- 
stant to  be  found  by  experiment,  or  by 


(11) 


varying  as  the  quantity  |/f 0.96— ^  --  ij;  while  the  density 
varies  as  I  -=-  Tlt  and  the  weight  flowing  per  second  varies  as 
the  product  of  velocity  and  density,  or  as--y  (0.96  7^  —T9). 

•L  \ 

This  becomes  a  maximum,  Tl  varying,  as  first  indicated  by 
Peclet,*  when 


,  Vo.967;  -  T, 
du  T,  2T, 


and 


*  Peclet,  vol.  i.  p.  166. 
21 


322  7^HE   STEAM-BOILED. 

or,  as  Rankine  states  it,*  7^  -f-  T^  =  f  f,  nearly;  and  the  most 
effective  draught,  but  not  the  most  economical,  is  obtained 
when  the  absolute  temperature  of  the  flue-gases  is  2.08 
times  that  of  the  atmosphere,  or,  as  c.lready  stated,  ordinarily 
about  550°  Fahr.  (288°  Cent.)  above  that  of  the  latter,  and 
their  density  is  about  one  half  that  of  the  atmosphere,  and 
the  volume  discharged  about  twenty-six  feet  per  pound.  For 
maximum  efficiency  of  apparatus  and  economy  of  fuel  the 
temperature  must  be  made  as  low  as  possible. 

In  constructing  grates  for  boilers  the  air-spaces  should  be 
made  as  narrow  as  is  practicable,  the  bituminous  coals  requir- 
ing more  air-space  than  anthracite.  A  half-inch  is  usually  con- 
sidered a  minimum  and  three  fourths  a  maximum.  The  area 
of  grate  should  be  somewhat  more  for  wood  than  for  coal,  the 
same  power  being  demanded. 

158.  The  Size  and  Design  of  the  Chimney,  its  height 
and  area  of  flue,  are  modified  somewhat  by  its  form  and  pro- 
portions, and  by  the  character  of  its  interior  surfaces.  The 
greater  the  friction-head  the  less  its  effectiveness.  A  chimney 
of  circular  section  and  with  a  straight  uniform  flue  is  better 
than  with  any  other  section  or  with  less  direct  flue.  The  flue- 
area  is  either  uniform  or  tapering  toward  the  top,  in  which 
latter  case  the  area  for  calculations  is  measured  at  the  top. 
Mr.  Kent  assumes  that  the  friction  may  be  taken  as  equivalent 
to  a  reduction  of  section  of  two  inches  all  around,  and  a  square 
flue  section  as  equivalent  to  a  circular  one  of  diameter  equal  to 
its  side.f  He  thus  obtains  the  following:  Assuming  a  commer- 
cial horse-power  to  demand  the  consumption  of  5  pounds  of 
coal  per  hour,  we  have  the  following  formulae  : 

0.    HP 

.     ....     .     .     (i) 


_  .     .     .     ...     .     (2) 

*=  12*^+4;  .......     (3) 

d=  13.541/^  +  4;  ......     (4) 


*  Steam-engine,  p.  289. 

f  Trans.  Am.  Soc.  M.  E.  1884. 


THE  DESIGN   OF   THE   STEAM-BOILER, 


323 


in  which  HP=  horse-power;  H=  height  of  chimney  in  feet; 
E  =  effective  area,  and  A  =  actual  area  in  square^feet ;  5=  side 
of  square  chimney,  and  d?=dia.  of  round  chimney  in  inches. 
The  following  table*  is  calculated  by  means  of  these  formulae : 

SIZES  OF  CHIMNEYS  AND   HORSE-POWER  OF   BOILERS. 


•sj 

HEIGHT  OF  CHIMNEYS,  AND  COMMERCIAL  HORSE-POWER. 

°?£ 

4J 

51  5oft 

60  ft 

70  ft. 

Soft. 

90  ft. 

100  ft. 

1  10  ft. 

125  ft. 

150  ft. 

175  ft. 

200  ft. 

Eg." 

C/3  ».S 

^"i-l^ 

18 

23 

25 

38 

27 

16 

0.97 

1.77 

24 

54 

S8 

62 

22 

2.08  -  3.14 

27 

6" 

72 

78 

83 

2    78           i    n8 

3° 

84 

92 

100 

107 

"3 

27 

3.58 

4.91 

P 

"5 
141 

125 

^63 

141 

I72 

3° 
32 

4.48 

5-47 

5-94 
7.07 

182 

.. 

39 

i8i 

IQ^ 

208 

219 

35 

6-57 

8.30 

42 

216 

231 

245 

258 

271 

.. 

.. 

38 

7.76 

9.62 

48 

311 

348 

3^5 

3«9 

43 

10.44 

12  57 

£ 

427 

536 

449 

472 

593 

503 
632 

692 

748 

54 

16^98 

15.90 
19.64 

66 

694 

728 

776 

849 

918 

98T 

59 

20.83 

23.76 

72 

835 

876 

934 

1023 

1105 

1181 

64 

25.08 

28.27 

78 

1038 

1107 

1212 

I3IO 

1400 

70 

29-73 

33-i8 

•84 

1214 

1294 

I4l8 

1531 

1637 

75 

34.76 

38.48 

90 

1496 

1639 

1770 

'893 

80 

40.19 

44-18 

96 

l876 

2027 

2167 

86 

46.01 

50.27 

The  external  diameter  at  the  base  should  be  one  tenth  the 
height,  unless  it  be  supported  by  some  other  structure.  The 
"  batter"  or  taper  of  a  chimney  should  be  from  T3^  to  J  inch  to 
the  foot  on  each  side. 

The  thickness  of  brick-work  should  be,  usually,  one  brick 
(8  or  9  inches)  for  25  feet  from  the  top,  increasing  \  brick  (4  or 
4J  inches)  for  each  25  feet  from  the  top  downwards.  If  the 
inside  diameter  exceed  5  feet  the  top  length  should  be  i£ 
bricks,  and  if  under  3  feet  it  may  be  \  brick  for  ten  feet. 

To  find  the  maximum  draught  for  any  given  chimney,  the 
heated  column  being  612°  F.,  and  the  external  air  62°  : 

Multiply  the  height  above  grate  in  feet  by  .0075,  and  the 
product  is  the  draught-power  in  inches  of  water. 

For  natural  draught  it  is  found  that  the  weight  in  pounds 
of  anthracite  coal  which  can  be  burned  on  the  square  foot  of 
grate  per  hour  is,  as  a  maximum,  for  example,  under  the  best 
conditions  in  marine  boilers, 


*"  Steam,"  1885. 


324  THE   STEAM-BOILER. 

F=2  V7f—  I,  nearly;     .....     (6) 

* 
and,  under  more  ordinary  conditions, 

P=!.SVff-i  ........    (7) 

From  this  we  obtain  the  following  : 

HEIGHTS  OF  CHIMNEY  AND  RATES  OF  COMBUSTION. 

Chimney-section  =  \  to  £  grate-area. 
Fuel,  Anthracite.  Best  Conditions. 


4 

H  =  height  of  chimney  in  feet  ;  W=  weight  of  coal  burned 
per  square  foot  of  grate  per  hour. 
Thus  for 

H=    50,  W=is; 

ff=    65,  W=i$; 

H=    80,  W=  17; 

H=  100,  £F=  19. 

These  figures  represent  very  exactly  the  results  of  Isher- 
wood's  experiments*  with  anthracite  coals. 

The  best  Welsh  and  Maryland  semi-anthracites,  or  good 
bituminous  and  semi-bituminous  coals,  should  give,  as  maxima, 


F=  2.25 
and  the  less  valuable  soft  coals,  more  nearly 


Thus,  average  coals  of  each  quality  stand,  relatively,  nearly 
as  follows  : 

Weight  per  Sq.       Area  Grate 
Foot  Grate.  per  Pound. 

Good  anthracite  coals  i.oo  i.o 

"      semi-anthracite  and  bitum.  1.05  0.9 

Ordinary  low-grade  coals,  soft  1.5  0.7 

"           "       "       anthracite  0.9  i.i 

*  Trowbridge,  Heat  and  Heat-engines,  N.  Y.,  1874;  Isherwood,  Researches 
in  Engineering. 


THE   DESIGN  OF    THE   STEAM-BOILER.  325 

Some  of  the  soft  coals  will  burn  still  more  freely,  while  some 
anthracites  will  burn  even  less  rapidly  than  above  stated.  The 
figures  given  may  be  taken  as  fair  averages.  The  height  of 
chimney  being  known  in  advance  or  settled  upon,  the  total 
quantity  of  fuel  to  be  burned  determines  the  area  of  grate. 
This  total  quantity  is  known  from  the  chemical  constitution  of 
the  fuel,  or  by  experiment  under  denned  conditions,  and  from 
the  work  demanded  and  the  intended  efficiency  of  the  boiler, 
as  estimated  by  the  methods  already  described. 

Mr.  Lowe,  a  builder  of  large  experience,  finds  the  following 
good  proportions*  for  stationary  boilers,  presumably  allowing 
about  30  pounds  of  water  per  hour,  and  15  square  feet  of 
heating-surface  per  horse-power  : 

STEAM-BOILER   CHIMNEYS. 
Heights  in  feet  .......................      50       60         70         80         90        100 

Sq.  in.  area  per  H.P  ....................       9      8.67      8.34     8.01      7.68      7.35 

Heights  in  feet  ..............    .........  no       120       130       140       150 

Sq.  in.  area  per  H.P  ....................  7.02      6.69      6.36     6.03      5.70 

Heights  in  feet  .......................  160       170       180       190       200 

Sq.  in.  area  per  H.P  ....................  5.37      5.04     4.71      4.38      4.05 

Professor  C.  A.  Smith  f  gives  the  following  formulas  for  the 
relation  of  height  of  chimney  to  fuel  consumption  : 


- 

4/77'  -77- 

where  If  is  the  height  of  chimney  in  feet,  A  its  flue-section 
in  square  feet,  and  ^Pthe  pounds  of  coal  burned  per  minute. 

Mr.  J.  T.  HenthornJ  gives  the  following  tables  of  dimen- 
sions of  chimney  as  obtained  by  the  empirical  formula: 

I2°G  -  A- 


in  which  he   takes  the   area,  G,  of  grate   in   square  feet,  the 
height,  H,  in   feet,  and  the  area  of   flue,  A,  in   inches.     It   is 

*  Am.  Machinist,  March  27,  1886. 
\Am.  Engineer,  Sept.  21,  1883,  p.  123. 
\  Journal  of  Commerce,  July  5,  1884. 


326 


THE   STEAM-BOILER. 


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328 


THE   STEAM-BOILER. 


assumed,  as  in  common  practice,  that  the  plain  cylindrical 
boiler  on  an  average  will,  when  supplying  a  good  engine  with 
detachable  valve-gear,  require  about  4.7  square  feet  of  heating- 
surface  for  actual  indicated  horse-power,  and  the  tubular  boiler 
1 1. 8,  the  two  boilers  giving  2.1  and  3  horse-power,  respectively, 
per  square  foot  of  grate. 

The  following  figure  is   the  graphic  representation  of  the 


130 


120 


110 


wo 


* 

a  so 

O 


70 


40- 
30 
2O 
JO 


DIAGRAM  FOR  HEIGHT 
OF  CHIMNEYS. 


I  '    1 

GRATE  SURFACE  CONNECTED,  IN  3O  FT. 


-140 


O  O 

O  O 


HORSE  POWER  :  •  GRATE  SURFACE  X  3  H.  R 

FIG.  73.—  DIMENSIONS  OF  CHIMNEY. 


law  of  variation  of  height  with  power  required  or  size  of  boiler, 
as  algebraically  given  in  the  formula  above. 

In  building  the  chimney  for  ordinary  use    in    connection 


THE  DESIGN  OF   THE   STEAM-BOILER. 


329 


with  steam-boilers,  the  fire-brick  lining  needed,  at  its  lower 
part,  when  receiving  gases  from  metallurgical  or  mill  furnaces, 
is  not  required.  The  centre-line  is  fixed  on  the  ground  and 
preserved  vertical,  while  under  construction,  by  the  use  of  a 
"  plumb-line,"  preferably  of  fine  brass  wire,  with  a  very  heavy 
"  bob"  steadied  by  immersion  in  a  pail  of  water,  molasses,  or 
other  liquid. 

The  shell  should  rarely  be  less  in  thickness  than  the  length 
of  a  brick  at  the  top,  and  the  lining  not  less  than  one  half  that 
thickness ;  this  thickness,  outside,  should  be  increased  by  the 
width  of  a  brick  at  every  interval  of  50  or  60  feet  from  the  top, 
the  lining  being  kept  approximately,  as  near  as  may  be,  at  one 
half  the  thickness  of  the  main  wall. 

The  great  chimney  at  St.  Rollox.  Glasgow,  of  the  height  of 
45  5i  feet,  has  the  following  dimensions  : 


Division 

of  the 
Chimney. 

Height  above 
Ground. 

Outer  Diameter 
in  Feet. 

Thickness  of  the  Wall  in 

Feet        and     Inches. 

4354 

134 

) 

V. 

[           I 

2 

3504 

i6£ 

\ 

) 

IV. 

I 

6 

1 

1 

210^ 

24 

) 

1 

III.        • 

! 

f      ' 

10* 

II. 

i 

114 

30 

1      2 

3 

544 

35 

) 
i 

I. 

2 

74 

i 

0 

40 

) 

The  foundation  of  this  chimney  has  a  depth  of  20  feet  and 
a  diameter  of  50  feet.  It  has  stood  safely  and  has  worked  sat- 
isfactorily for  nearly  a  half-century,  and  may  be  looked  upon  as 
a  good  example  of  successful  construction. 

159.  Forms  and  Proportions  of  Furnace  and  Grate 
are  settled  upon  so  soon  as  the  character  of  the  fuel  and  the 
proportions  of  chimney  are  fixed. 

The  rate  of  combustion  is  fixed,  as  a  maximum,  as  already 
seen,  by  the  height  of  chimney ;  minimum  rates  are  anything 


330  THE   STEAM-BOILER. 

less,  and  the  customary  rates  may  be  taken  as  not  far  from  the 
following. 

The  rate  of  combustion  of  coal  in  a  furnace  is  usually  stated 
in  pounds  per  hour,  burned  on  each  square  foot  of  grate. 

Pounds  per 

WITH   CHIMNEY-DRAUGHT.  square  foot 

per  hour. 

1.  The  slowest  rate  of  combustion  in  Cornish  boilers. ...     4  to    6 

2.  Ordinary  rate  in  these  boilers 10  to  15 

3.  Ordinary  rates  in  factory  boilers  12  to  18 

4.  Ordinary  rates  in  marine  boilers 15  to  25 

5.  Quickest  rates  of  complete  combustion  of  anthracite 

coal,  the  supply  of  air  coming  through  the  grate 

only 15  to  20 

6.  Quickest  rates  of  complete  combustion  of  bituminous 

coal,  with  air-holes  above  the  fuel  -fa  the  area  of 

grate 20  to  25 

FORCED   DRAUGHT. 

7.  Locomotives 40  to  TOO 

8.  Torpedo-boats , 60  to  125 

Fuels  of  the  several  classes  should  evaporate,  respectively, 
from  feed-water  at  the  boiling-point  and  at  atmospheric  pres- 
sure, under  the  most  favorable  possible  conditions,  about  as  fol- 
lows : 

Weight  water 
Relatively.  per  unit 

weight  of  fuel. 

Best  anthracite 100  13.5 

Best  semi-anthracite  and  bituminous. .  no  15 

Ordinary  coals,  soft 80  n 

Ordinary  coals,  anthracite 75  10 

Examples  of  these  several  classes  are  seen  in  the  best 
Pennsylvania  anthracites,  the  Welsh  and  Maryland  semi-anthra- 
cites, or  semi-bituminous  coals,  the  ordinary  good  bituminous 
fuels  of  Nova  Scotia  and  of  Western  Pennsylvania,  and  the 
earthy  coals  of  the  West. 

The  quantity  of  steam  actually  made  will  depend  upon  the 
temperature  of  the  feed-water,  and  will  be  less  as  the  water  is 
colder.  It  is  customary,  as  elsewhere  stated,  to  reduce  the 
results  of  experiments  determining  efficiency  of  boilers  to 


THE  DESIGN  OF   THE   STEAM-BOILER.  33! 

"  equivalent  evaporation  from  and  at  the  boiling-point,"  under 
atmospheric  pressure. 

When  the  maximum  possible  evaporation  is  given  for  feed 
at  212°  F.  (100°  C),  and  at  atmospheric  pressure,  i.e.,  under  the 
standard  conditions,  multiplying  that  figure  by  the  reciprocal 
of  the  factor  of  evaporation  for  the  proposed  temperatures  of 
feed  and  of  steam  will  give  the  maximum  possible  evaporation 
under  the  latter  conditions.  Thus  we  get  the  following : 

RELATIVE  EVAPORATION  AT  VARYING  TEMPERATURES  OF  FEED. 

Temperature      of)  212°  F.  200      180      160      140      120      100      80      60      40 

feed-water )  100°  C.     93.3     82.2     71.1     60.0     48.8     37.7  26.6  15.5     4.4 

Relative    steam 


100  98        96        94        92        90        88      87      86      84 

evaporation.. ..  ) 

The  coals  in  common  use  in  the  United  States  are : 

The  semi-bituminous  coals  from  Maryland* 

The  anthracites  from  Pennsylvania. 

The  bituminous  coals  from  Pittsburg  and  Western  Pennsylvania. 

The  bituminous  coals  from  Ohio  and  the  West. 

When  burned  in  ordinary  furnaces,  these  coals  will  make 
steam,  per  pound  of  coal,  in  nearly  the  following  proportions, 
as  given  by  Mr.  T.  Skeel  :* 

Semi-bituminous no 

Anthracite « 100 

Pittsburg 90 

Ohio 75 

The  weights  that  may  be  burned  on  the  same  grate,  with 
the  same  chimney,  will  vary  nearly  as  follows : 

Anthracite 100 

Semi-bituminous I2O 

Pittsburg , 120 

Ohio 200 

Relative  areas  of  grate-surface  that  will  be  necessary  to 
burn  coal  enough  to  furnish  the  same  quantity  of  steam  are 
nearly  as  follows : 

*  Weisbach,  Vol.  II. 


332  THE   STEAM-BOILER. 

Anthracite , 100 

Pittsburg 90 

Semi-bituminous 75 

Ohio 67 

This  refers  to  the  average  coal  of  each  kind  in  practice. 

The  loss  as  refuse  falling  through  well-proportioned  grate- 
bars  may  be  taken  as  5  to  10  per  cent  for  good  bituminous 
coals,  or  10  to  20  per  cent  for  the  lower  grades,  and  about  the 
same  for  anthracites.  Wood  may  be  taken  by  weight  as  hav- 
ing one  half  the  value  of  coal.  A  cord  of  best  hard  wood 
should  equal  a  ton  of  good  coal. 

From  the  results  of  chemical  analyses,  the  evaporative 
power  of  various  kinds  of  fuel,  expressed  in  pounds  of  water 
per  pound  of  fuel  evaporated  from  and  at  212°  F.,  which  we 
will  call  E,  has  average  values  given  by  Prof.  C.  A.  Smith*  in 
the  following  table,  which  may  be  found  useful,  as  supplement- 
ary to  the  several  other  sets  of  data  already  given  in  this  con- 
nection. 

Kinds  of  Fuel.  E 

Pure  carbon  completely  burned  to  CO2 15 

Pure  carbon  incompletely  burned  to  CO 4.5 

CO  completely  burned  to  CO2 10.5 

Charcoal  from  wood,  dry 14 

Charcoal  from  peat,  dry 12 

Coke  good,  dry .' 14 

Coke  average,  dry 13.2 

Coke  poor,  dry 12.3 

Coal,  anthracite 15-3 

Coal,  dry  bituminous,  best 15.9 

Coal,  bituminous 14 

Coal,  caking,  bituminous,  best 16 

Coal,  Illinois  (from  four  mines  near  St.  Louis) 12 

Lignite 12.1 

Peat,  dry 10 

Peat  with  one  fourth  water 7.5 

Wood,  dry 7-25 

Wood  with  one  fifth  water 5.8 

Wood,  best  dry  pitch-pine 10 

Mineral  oils,  about  22.6 

*  Am.  Engineer,  1883. 


THE  DESIGN  OF   THE   STEAM-BOILER.  333 

The  anthracite  coals  burn  completely  with  a  thin  fire  and 
excess  of  air,  but  should  have  a  thickness  pretty  nearly  propor- 
tional to  the  rate  of  combustion,  a  good  proportion  being  about 
one  foot  thickness  on  a  rate  of  combustion  of  20  pounds  on  the 
square  foot  of  grate  per  hour  (i  decimetre  per  65  kilogs.  on  the 
square  metre).  The  bituminous  coals  will  not  burn  well  ex- 
cept in  a  thick  bed  and  at  high  temperature,  and  when  re- 
moved from  the  chilling  influence  of  "adjacent  cold  iron.  A 
hot  fire  and  large  space  for  combustion  are  here  essential. 
The  furnace  may  therefore  be  of  less  capacity  with  hard  than 
with  soft  coals ;  but  a  good  height  over  the  grate  and  a  large 
combustion-chamber  are  very  desirable  with  the  latter,  and  are 
of  advantage  in  all  cases.  A  fire-brick  furnace,  or  an  arch  of 
brick-work  over  the  grate,  gives,  some  gain  usually. 

The  rate  of  combustion  to  be  anticipated  and  the  intended 
efficiency  of  boiler,  and  evaporation  per  unit  weight  of  fuel 
being  ascertained,  the  area  of  grate  is  at  once  calculable  by 
dividing  the  total  weight  of  steam  to  be  supplied  by  the  evapo- 
ration to  obtain  the  weight  of  fuel  to  be  needed,  and  then  di- 
viding this  total  weight  per  unit  of  time  by  the  quantity  to  be 
burned  on  a  unit  area  of  grate.  Thus,  1000  horse-power 
being  called  for,  at  30  pounds  (13.6  kilogs.)  per  H.  P.  per  hour, 
30,000  pounds  (1361  kilogs.)  of  steam  are  demanded  per  hour. 
At  10  pounds'  evaporation  and  10  pounds  burned  on  the  square 
foot  (48.8  kilogs.  on  the  square  metre)  of  grate-surface,  300 
square  feet  (27.9  square  metres)  of  grate  must  be  provided, 
which  would  usually  be  divided,  for  convenience  in  construc- 
tion and  operation,  between  several  furnaces,  as  furnaces  of 
greater  depth  than  about  6  feet  (1.8  m.)  cannot  be  easily 
handled,  that  being  about  as  far  as  coal  can  be  well  thrown ; 
while  a  greater  width  than  3  or  4  feet  (0.9  to  1.2  m.)  introduces 
difficulties  of  construction. 

The  "  combustion-chamber,"  which  usually  forms  a  part  of 
a  well-designed  furnace,  may  be  either  simply  an  enlargement 
of  the  height  of  the  furnace  itself  to  obtain  the  space  and  time 
needed  by  the  gas-currents  for  complete  intermixture  and  thor- 
ough combustion,  or  it  may  be  any  separate  chamber  beyond 
the  grate.  The  latter  is  often  the  best  method  of  securing  the 


334  THE  STEAM-BOILER. 

desired  results  ;  but  the  more  usual  plan  is  that  of  giving  con- 
siderable height  of  furnace-crown. 

Grate-bars  are  spaced  differently  for  different  kinds  of  fuel. 
Thus,  for  fine  "  pea"  anthracite  coal,  the  spaces  between  the 
bars  are  usually  made  about  a  quarter  of  an  inch  (0.6  cm.)  ;  for 
"chestnut,"  f  inch  (0.9  cm.);  for  "  stove"  coal,  \  inch  (1.27 
cm.)  ;  and  for  large  anthracite  and  for  bituminous  coals,  f  to  f 
inch  (0.95  to  1.9  cm.)  ;  while  wood-burning  calls  for  an  inch 
(2.56  cm.). 

160.  The  Relative  Areas  of  Chimney,  Flues,  and  Grate 
are  seen  to  be  variable  with  the  circumstances  under  which  -the 
boiler  is  to  be  operated,  but  with  natural  draught  and  usual 
working  conditions  certain  proportions  have  become  almost 
universally  accepted  as  standard  in  common  practice.  Thus 
it  may  be  taken  as  well  settled  by  experience,  that  in  chimneys 
of  circular  section,  smooth  internal  surfaces,  and  in  the  open, 
where  draught  is  unobstructed  by  air-currents  produced  by 
surrounding  objects,  as,  for  example,  with  marine  steam-boilers, 
the  minimum  ratio  of  chimney-flue  section,  section  through  the 
tubes  and  that  over  the  bridge-wall  to  grate-surface  should  be, 
at  least,  respectively,  ^,  -J,  ^,  while  a  maximum  to  be  adopted 
with  forced  draught  is  not  far  from  1,  -J-,  and  -J-,  for  anthracite 
coal.  The  latter  ratios  will  also  work  well  for  bituminous,  free- 
burning,  coals  and  natural  draught ;  and  the  sections  may  often 
be  made  still  greater,  with  advantage  when  a  blast  is  also  used 
with  such  fuel. 

With  restricted  draught-area  the  amount  of  fuel  that  may 
be  burned  becomes  reduced  ;  thus,  assuming  a  chimney  50  feet 
(16  m.)  high  : 

Area  of  least  flue-section  (grate  =  i)  ...  0.14        o.io        0.07  0.05  0.04 

Relative  coal  burned I.  .      0.8  0.7  0.6  0.4 

Average  fuel,  Ibs.  per  sq.  ft.  grate 15  12  10  9  6 

"     kilogs.  per  sq.  m 7.5  6  5  4.5  3 

For  square  sections  of  chimney-flue  and  with  rough  interior 
surfaces  the  size  of  chimney  is  increased  both  in  weight  and 
area  of  section.  As  a  general  rule,  the  height  of  factory  chim- 
neys is  increased  with  the  size  and  number  of  boilers,  irrespec- 


THE  DESIGN  OF   THE   STEAM-BOILER.  335 

tive  of  the  above-stated  ratios,  and  a  not  uncommon  proportion 
of  "  stack"  is  that  which  makes  the  height  about  twenty  times 
the  diameter  of  the  flue.  Ordinary  mill-chimneys,  for  moder- 
ate powers,  range  between  50  and  75  feet  (16  and  23  m.)  in 
height. 

161.  Common  Proportions  of  Boiler  are  found  in  ordinary 
practice  to  be  not  far  from  those  given  below. 

The  interior  space  of  the  boiler  is  commonly  divided  into 
about  two  thirds  or  three  fourths  water-space,  the  remainder 
being  steam-room.  In  marine  boilers  more  steam-space  should 
be  given. 

RATIO   OF  HEATING    TO   GRATE  SURFACE. 

Plain  cylinder  boilers 12  to  15 

Cornish ...  15  to  30 

Cylindrical  flue 20  to  25 

tubular , 25  to  35 

Marine  tubular  (fire) 30  to  35 

(water) 3510  40 

Locomotive  tubular 50  to  100 

The  ratio  of  heating  to  grate  surfaces  should,  where  possible, 
be  always  carefully  determined  with  reference  to  maximum  com- 
mercial efficiency  in  the  manner  described  in  a  later  chapter. 

The  above  proportions  produce  ratios  of  weights  of  fuel 
burned  per  unit  area  of  heating-surface,  in  general  practice, 
about  as  follows : 


RATIO  OF   FUEL   BURNED   TO   HEATING-SURFACE. 


Pounds  per 
sq.  ft.  H.  S. 

Kilogs.  per 
sq.  in. 

Stationary  boilers     .        .  .                      

05  to  i  o 

O  I    to   O  2 

o  5  to  o  6 

o  i  to  o  3 

Locomotive  and  forced  draught 

o  8  to  i  o 

o  A  to  o  ^ 

Similarly,  the  power  of  such  boilers  may  be  reckoned 
roughly  as  below,  and  their  relative  standing  in  efficiency  and 
capacity  taken  as  follows : 


336 


THE   STEAM-BOILER. 
HORSE-POWER   AND  ECONOMY. 


PER  H.  P. 

RELATIVE  STANDING. 

Sq.  ft. 

Sq.  in. 

Capacity. 

Economy. 

Water  tube     

IO  to  12 

14  to  18 
8  to  12 
6  to  10 

I   tO      2 

i.o  to  i.i 
1.3  to  1.6 
0.7  to  i.i 
o  5  to  0.9 

O.I  to  O.2 

I. 

0-75 
0.50 
0.  2O 

0.6 

I. 
0.9 

0  3 
0.7 
0.8 

Fire-tube  

Flue  

Plain  cylindrical 

Locomotive         

The  above,  as  with  every  proportion  and  detail  of  the  steam- 
boiler,  should  always  be  made  the  subject  of  careful  calculation 
whenever  the  case  is  in  the  least  degree  peculiar. 

The  following  are  proportions  frequently  accepted  by  the 
trade  for  the  two  most  common  varieties  of  stationary  boiler 
sold  in  the  market: 


PROPORTIONS   OF  CYLINDRICAL  TUBULAR   BOILERS. 


FLUES. 

DOME. 

STACK. 

T3 

1 

4 

i 

a 

HI 

y 

•a 

§    , 

.G 

o 

1 

u 

I 

1 

c/3 

03 
4J 

DC 

8 

a! 
C 

75 

I 

|[g 

175 

Q 

V 

i 

"J 

!j 

c 

T 

<u 

c 

T 

C 

08 

°| 

£s 

G 

T 

i 

Sf 

ff| 

U 

a 

1| 

u 

T 

V 

1 

£"5 

<u  £ 

0"*- 

u 

i 

o  1 

°  3;j 

Q 

1 

1 

g 

1 

.c 
be 

1 

o 

•i"" 

J^ 

be 

V 

1 

be 

11 

Jc  >< 

3 
fc 

1 

CO 

5 

f 

Q 

3 

Q 

'v 

K 

H 

H 

3 

Q 

'C 
I 

!§. 

^ 

I 

15 

36 

8'  ii 

30 

3 

8 

20 

20 

H 

% 

3 

18 

26 

2,950 

5,350 

2 

20 

36 

10'  ii 

30 

3 

10 

20 

20 

/4 

% 

3^ 

18 

30 

3,500 

5.900 

3 

25 

42 

1  1' 

38 

3 

10 

24 

24 

?% 

% 

3/^ 

20 

30 

4,400 

7.100 

4 
5 

3° 

35 

42 

44 

$ 

38 
46 

3 
3 

12 
12 

24 
24 

11 

% 

4 

4 

2O 
22 

36 
36 

5,000 

5,500 

7,800 
8,700 

6 

40 

48 

13'     2 

52 

3 

12 

24 

28 

% 

24 

36 

6,400 

9,900 

7 

45 

50 

14        2 

52 

3 

13 

30 

3° 

% 

24 

36 

6.800 

10,400 

8 

50 

54 

13'      2 

58 

3 

12 

3° 

30 

% 

26 

36 

7,600 

11.500 

9 

60 

54 

16'    2 

58 

3 

15 

30 

30 

% 

<  ^3 

26 

45 

8,550 

12.750 

10 

70 

60 

J5'    4 

76 

3 

30 

30 

T?B 

'  /^ 

28 

45 

10,000 

14,500 

ii 

75 

60 

16'    4 

76 

3 

15 

30 

30 

T?B 

'  ^2 

28 

5° 

10.500 

15.100 

12 

80 

60 

*7'    4 

76 

3 

16 

30 

36 

TB 

5 

28 

55 

n,2oo 

1  6,  TOO 

13 

90 

66 

16'     5 

100 

3 

15 

36 

36 

•J^ 

5 

32 

55 

13,500 

19.100 

100 

66 

J7'    5 

100 

3 

16 

36 

36 

^B 

5 

32 

55 

14,200 

19,800 

15 

125 

72 

17'    6 

132 

3 

16 

36        36 

? 

5 

36 

60 

17,200 

24,000 

The  upright  tubular  boiler  is  given  less  heating-surface 
than  the  above,  is  much  lighter,  and  is  less  economical.  The 
locomotive  type  of  stationary  boiler  has  about  the  same  weight 
as  the  above,  but  rather  less  heating-surface. 


THE  DESIGN  OF   THE   STEAM-BOILER.  337 

According  to  Professor  Rankine,*  a  very  useful  mode  of  com- 
paring  the  capacities  of  different  boilers  is  to  divide  the  boiler- 
space  by  the  area  of  heating-surface,  and  thus  is  obtained 
a  mean  depth.  Of  the  following  examples,  the  first  three  are 
given  on  the  authority  of  Mr.  Fairbairn's  "  Useful  Information 
for  Engineers:" 

"  Mean  depth." 
Feet. 

Plain  cylindrical  egg-ended  boiler,  with  external  flues  below  and 

at  each  side,  but  no  internal  flues 3. 50 

Cylindrical  boiler  with  external  flues,  and  one  cylindrical  internal 

flue ,' 1.65 

Cylindrical  boiler  with  external  flues,  and  two  cylindrical  internal 

flue i.OO 

Stationary  boilers  according  to  Mr.  Robert  Armstrong's  rules  .  .     3.00 

Multitubular  marine  boilers,  about 0.50 

Locomotive  boilers,  and  boilers  composed  of  water-tubes,  aver- 
age about : .     o.  10 

Boilers  of  large  size  and  capacity  exhibit  steadiness  in  the 
pressure  of  the  steam,  ready  deposition  of  impurities,  space  for 
the  collection  of  sediment,  and  freedo'm  from  priming.  Those  of 
small  capacity  excel  in  rapid  raising  of  the  steam  to  any  required 
pressure,  small  surface  for  waste  of  heat,  economy  of  space  and 
weight,  of  special  importance  on  board  ship,  greater  strength 
with  a  given  quantity  of  material,  and  smaller  damage  in  the 
event  of  an  explosion. 

Mr.  D.  K.  Clark  considers  that  we  may,  in  ordinary  loco- 
motive practice,  take  the  economical  consumption  of  fuel  as 
proportional  to  the  square  of  the  area  of  heating-surface,  and 
make  the  grate-area  vary  in  the  same  proportion.  He  adopts- 
nine  to  one  as  the  standard  and  desirable  evaporation  of  water 
as  compared  with  weight  of  fuel,  makes  the  maximum  and 
minimum  allowable  rates  of  combustion  150  and  14  pounds  per 
square  foot  of  grate,  and  the  maximum  evaporation  in  loco^ 
motive  boilers  about  22  cubic  feet  per  hour.f  A  rate  of  com- 
bustion of  112  pounds  is  considered  a  practical  maximum,  the 
ratio  of  heating  to  grate  surface  being  85  to  I. 

*  Steam-engine  and  Prime  Movers, 
f  Railway  Machinery,  p.  165. 
22 


33§  THE   STEAM-BOILER. 

162.  The  Usual  Rates  of  Evaporation  and  the  effect  of 
varying  the  proportions  of  tubes  has  been  well  determined  by 
the  experiments  of  Isherwood  and  others. 

The  proportions  of  flues  and  tubes  vary  somewhat  in  prac- 
tice ;  but  it  will  be  found  seldom  advisable  to  make  tubes  more 
than  50  or  60  diameters  in  length.  Where  the  heating-surface 
consists  principally  of  tubes,  the  efficiency  will  be  found  to  vary 
with  their  length  nearly  as  follows : 

Length  of  tube  (diameters). ...   ...  60         50        40         30         20 

Water  per  unit  weight  of  fuel 12       n         10          9  S 

When  the  ratio  of  heating  to  grate  area  was  25  to  i,  Isher- 
wood found  the  evaporation  to  vary  thus: 

Fuel  per  hour 8  10          12          16          20          24 

Evaporation 10  5         10.1         9.5         8.2         7.3         6.8 

which  series  is  represented  by 

W  —  ^— =  ,  nearly. 
vr 

Clark  obtained  with  locomotives  an  equal  evaporation  with 

Fuel  (coke) 15    25    38    56    76    98    125    153 

Ratio  of  H.  S.  to  G.  S 30    40    50    60    70    So    90    100 

the  evaporation  being  constant  at  9  of  water  to  I  of  fuel,  which 
may  be  expressed  by 

S  =  SVF,  nearly, 

5  being  the  ratio  of  the  two  areas  and  F  the  weight  of  coke 
burned  on  the  unit  of  area  of  grate. 

In  estimating  area  of  heating-surfaces  the  whole  surface 
exposed  to  the  hot-furnace  gases  is  reckoned.  The  formula 
for  efficiency  already  given  illustrates  the  progressive  variation 
of  the  evaporative  power  with  change  of  proportions  of  boiler. 

163.  The   Relation   of  Size    of   Boiler    to   Quantity  of 
Steam  demanded  is  one  that  occasionally  becomes  worthy  of 
consideration.     Where  the  steam  is  required  for  driving  steam- 
engines  it  is  very  important  that  it  should  be  thoroughly  dry, 
and  it  is  an  advantage  to  moderately  superheat  it.     Maximum 
economy  cannot  be  attained  where  wet  steam  is  used.     A  boiler 


THE   DESIGN  OF   THE   STEAM-BOILER.  339 

attached  to  a  steam-engine,  and  especially  where  fuel  is  costly 
and  efficiency  important,  should  have  ample  heating-surface, 
some  superheating-surface  if  practicable,  ample  extent  of  water- 
surface  area  to  permit  free  separation  of  steam  and  water,  and 
large  steam-space. 

Steam  employed  for  heating  purposes  is  not  necessarily  dry  ; 
it  may  carry  a  large  amount  of  water  with  it  into  the  system  of 
heating-coils  or  radiators,  and  yet  give  good  results,  if  the 
latter  are  of  large  section.  Where  the  pipes  are  of  restricted 
area  of  section,  however,  wet  steam  flowing  less  freely  than 
when  dry  or  superheated,  there  may  result  such  a  retarda- 
tion of  flow  and  of  circulation  as  may  cause  considerable 
increase  of  cost.  This  has  been  found  sufficiently  great,  in 
some  cases,  to  justify  drying,  and  perhaps  superheating,  the 
exhaust-steam  from  engines  where  used  for  heating  purposes. 
As  a  general  rule,  the  boiler  must  be  made  a  trifle  larger  to 
supply  perfectly  dry  steam  and  do  good  work. 

In  the  use  of  steam  for  heating  purposes,  one  square  foot 
of  boiler-surface  will  supply  from  7  to  10  square  feet  of  radiating 
surface.  Small  boilers  should  be  larger  proportionately  than 
large  boilers.  Each  horse-power  of  boiler  will  supply  from  250 
to  350  feet  of  i -in.  steam-pipe,  or  80  to  120  square  feet  of  radiat- 
ing surface. 

Under  ordinary  conditions  one  horse-power  will  heat  about — 

Brick  dwellings,  in  blocks,  as  in  cities 15,000  to  20,000  cub.  ft. 

"      stores          "       "        10.000  "  15,000  "  " 

"     dwellings,  exposed  all  around 10,000  "  15,000  "  " 

"     mills,  shops,  factories,  etc 7,000  "  10,000  "  " 

Wooden  dwellings,  exposed 7,000  "  10,000  "  " 

Foundries  and  wooden  shops   6,000  "  10,000  "  " 

Exhibition  buildings,  largely  glass,  etc 4,000  "  10,000  "  " 

The  system  of  heating  mills  and  manufactories  by  means  of 
pipes  placed  overhead  is  recommended. 

The  air  required  for  ventilation  is  usually  warmed  by  the 
"  indirect"  system  of  radiation,  the  current  passing  through 
boxes  or  chambers  in  which  a  sufficient  amount  of  pipe  is  coiled 
to  heat  it  well.  From  5  to  15  cubic  feet  per  individual  per 


340  THE    STEAM-BOILER. 

minute  are  allowed,  the  former  in  crowded  halls,  the  latter  in 
dwellings,  and  about  one  tenth  as  much  for  each  gas-burner  or 
lamp. 

164.  The  Number  and  Size  of  Boilers  to  be  used  in  any 
case  in  which  considerable  power  is  demanded  is  determined 
mainly  by  practical  considerations  related  to  their  construction. 
As  a  rule,  the  larger  boiler  is  more  economical  in  first  cost  and 
in  operation,  within  certain  limits,  than  several  smaller  boilers 
of  equal  aggregate  power.  But  passing  a  limit  which  cannot 
be  usually  very  exactly  defined,  expense  is  increased,  trans- 
portation becomes  difficult,  location  and  setting  involve  prob- 
lems difficult  of  solution,  and  management  becomes  less  easy. 
Mr.  Leavitt  has,  however,  constructed  stationary  boilers,  of  a 
peculiar  modification  of  the  locomotive  type,  of  as  high  as  one 
thousand  horse-power ;  and  marine  boilers  of  equal  or  greater 
power  have  been  built  not  infrequently  for  steamers  plying  on 
the  larger  rivers  of  the  United  States.  Stationary  boilers  of 
100  horse-power  and  marine  boilers  of  500  are  more  usual  and 
more  commonly  suitable  sizes.  Locomotive  boilers  are  neces- 
sarily always  sufficiently  large  to  supply  all  the  power  de- 
manded of  the  engine. 

The  type  of  boiler  has  much  influence  on  the  limit  of  size. 
Plain  "  cylinder  boilers"  are  rarely  made  more  than  from  3  to  4 
feet  (0.9  to  1.2  m.)  in  diameter,  and  this  restricts  the  grate- 
area  so  that  the  power  derivable  from  a  single  such  boiler  is 
seldom  more  than  15  or  20  horse-power,  and  is  usually  much 
less.  The  more  complex  structures  often  include  several  fur- 
naces, and  yield  from  100  to  200  horse-power  each  on  land,  and 
more  at  sea. 

Makers  in  the  United  States  usually  allow  15  square  feet  of 
heating-surface  and  one  of  grate  to  the  horse-power,  in  plain 
cylindrical  boilers,  and  the  same  area  of  heating-surface,  but  a 
fourth  and  a  half  less  grate-area,  respectively,  with  flue-boilers 
and  tubular  boilers,  where  estimating  for  the  market. 

M.  de  Pambour  found  the  priming  of  French  locomotive 
boilers  in  1834  to  amount  to  about  30  per  cent ;  M.  de  Chatel- 
lier,  in  1843-4,  found  it  to  be  30  to  50  per  cent;  but  a  large 
proportion  of  the  moisture  measured  was  undoubtedly  the 


THE  DESIGN  OF    THE   STEAM-BOILER. 


341 


product   of   cylinder  condensation,  for  which   loss   Clarke   al 
lowed  as  follows  :  * 


CONDENSATION. 

RATIO  OF  EXPANSION. 

Per  cent,  of  Steam 

Per  cent,  of 

indicated. 

Total  Steam. 

1.25 

12 

II 

1.67 

12 

II 

2  OO 

12 

II 

2.50 

21 

17 

3.67 

32 

24 

5.00 

46 

32 

8-33 

73 

42 

—which  figures  indicate  the  proportion  of  steam  by  weight  to 
be  added  to  that  calculated  for  the  ideal  engine,  to  obtain  the 
probable  requirement  of  the  real  engine. 

Builders  of  the  more  economical  classes  of  engines  supply 
them  with  boilers  often  of  less  size  than  the  accepted  standard 
rating  would  dictate,  as  they  demand  less  steam  per  horse- 
power than  the  average  engine.  A  good  engine  of  moderate 
size,  with  an  automatically  governing  and  adjusting  valve-gear, 
if  condensing,  should  give  good  results  on  as  low  as  seven  or 
eight  square  feet  of  heating-surface  per  actual  horse-power,  and 
if  non-condensing,  with  ten  or  twelve  square  feet.  Large  en- 
gines are  given  a  smaller  allowance  of  heating-surface,  propor- 
tionally, than  are  small  engines. 

165.  The  Standard  Sizes  of  Tubes  have  become  well  set- 
tled by  custom.  So  large  an  element  of  boiler-construction 
necessarily  assumes,  with  time,  a  somewhat  rigid  set  of  propor- 
tions. The  sizes  employed  range  from  I  or  I J  inch  (25.4  to 
3 1  mm.)  diameter  in  the  smallest  boilers,  to  2  or  2-J-  inches  (5 1  to 
63.5  mm.)  in  the  locomotive  and  other  boilers  of  moderate  size; 
and  to  3  or  4  inches  (76  or  102  mm.),  or  even  5  or  6  inches  (1.27 
or  1.52  mm.),  in  large  boilers,  or  where  a  very  free  draught  or 
greater  convenience  of  access  are  required.  Water-tube  boilers 


*  Railway  Machinery,  p.  144. 


342 


THE   STEAM-BOILER. 


are  commonly  given  tubes  4  or  5  inches  (102  or  127  m.)  in 
diameter.  The  length  of  the  tube  is  customarily  not  above  50 
or  60  diameters  in  stationary  boilers,  and  two  thirds  this  length 
in  marine  work.  The  spaces  between  the  tubes  should  be  about 
one  half  their  diameter  ;  they  are,  however,  usually  placed  much 
closer.  All  tubes  in  our  market  are  gauged  to  British  measures, 
as  below : 

When  the  dimensions  of  a  tubular  boiler  are  given,  the  out- 
side diameter  of  the  tubes  is  usually  stated,  so  that  twice  the 
thickness  must  be  subtracted  to  obtain  the  diameter  to  be  used 
in  the  calculation  of  heating-surface.  The  thickness  of  tubes 
by  different  makers  varies  somewhat,  but  those  given  below 
are  average  values,  and  can  be  used  without  serious  error.  The 
table  gives  dimensions  of  standard  sizes  of  tubes. 


STANDARD    TUBES. 


Outside 
diameter  in 
inches. 

Thickness  in 
inches. 

Internal  diameter 
in  inches. 

Internal  diameter 
in  feet. 

Heating-surface  in 
square  feet,  per 
foot  of  length. 

1.25 

0.072 

I.I06 

0.0922 

0.3273 

i-5 

0.083 

1-334 

O.III2 

0.3926 

i-75 

0.095 

1.560 

O.I3OO 

0.4589 

2. 

0.095 

1.810 

o.  1508 

0.5236 

2.25 

0.095 

2.060 

0.1717 

0.5890 

2-5 

o.  109 

2.282 

0.1902 

0-6545 

2-75 

0.109 

2.532 

0.2IIO 

0.7200 

3- 

0.109 

2.782 

0.2318 

0.7853 

3-25 

O.  1  2O 

3.010 

0.2508 

0.8508 

3-5 

O.  I2O 

3.260 

0.2717 

0.9163 

3-75 

O.  T2O 

3-510 

0.2925 

0.9817 

4- 

0.134 

3-732 

O.3IIO 

1.0472 

4-5 

0.134 

4.232 

0.3527 

1.1790 

5- 

0.148 

4.704 

0.3920 

1.3680 

6. 

0.165 

5.770 

0.4808 

1.5708 

7- 

0.165 

6.770 

0.5642 

1.8326 

8. 

0.165 

7.770 

0-6475 

2.0944 

9- 

O.lSo 

8.640 

0.7200 

2.3562 

10. 

O.2O3 

9-594 

0.7995 

2-5347 

The  following  are  the  dimensions  of  standard  tubes  as  made 
by  some  of  the  best  makers  in  the  United  States: 


THE  DESIGN  OF   THE   STEAM-BOILER. 


343 


LAP-WELDED  CHARCOAL-IRON  BOILER-TUBES. 
Standard  Dimensions. 


1 

i 

j. 

I 

i 

1 

a 

21 

£  C 

g 

|-a 

J^  . 

Si 

iS 

V 

^ 

c  . 

N 

K-3 

n\  C 

rt  "rt 

Sj 

£g 

o-S 

CO  £ 

s£ 

Ii 

X 
." 

O 

£  S 
6  £ 

&  i 

if 

|i 

u  c 

S.T 

S-I 

ff 

.2  * 

rt  c 
ft 

Si 

H 

1 

3  K 

3.S 

£  * 

c 

>  " 
c 

bt-5 

•S  " 

t 

o 

'° 

1 

H 

H 

1 

J^ 

^ 

* 

In. 

In. 

In. 

No. 

In. 

In. 

Sq.  in. 

Sq.  in. 

Sq.  in. 

Feet. 

Feet. 

Lbs. 

.86 

.072 

15 

3-H 

2.69 

•78 

•57 

.21 

3-82 

4.46 

•71 

125 

.98 

.072 

15 

3-53 

3-08 

•99 

•76 

•24 

3-39 

3-89 

.8 

•  25 

i.  ii 

.072 

15 

3-93 

3-47 

1.23 

.96 

•27 

3-o6 

3-45 

.89 

•32 
•375 

I.  21 

-083 
-083 

14 

4.12 
4  32 

3-6 
3-8 

1:3 

1.03 
i-i5 

•32 
•34 

2.91 
2.78 

3-33 
3.16 

.08 
•'3 

5 

J-33 

.083 

14 

4-71 

4.19 

1.77 

1.4 

•37 

2-55 

.86 

.24 

•  625 

1.43 

•095 

13 

4-51 

2.07 

1.62 

.46 

2-35 

.66 

53 

•75 

1.56 

•°95 

13 

5-5 

4-9 

2-4 

1.91 

•49 

2.18 

•45 

.66 

875 

1.68 

•095 

13 

5-89 

5-29 

2.76 

2.23 

•53 

2.04 

27 

.78 

1.81 

•095 

13 

6.28 

5-69 

3  14 

2  57 

•57 

1.91 

.  ii 

.91 

•  125 

1.93 

•°95 

13 

6.68 

6.08 

3-55 

2-94 

.61 

1.8 

•97 

.04 

•25 
•375 

2.06 
2.16 

•095 
.109 

12 

7.07 
7.46 

6.47 
6.78 

3-98 
4-43 

iS 

.64 
•78 

i!6i 

•85 
•77 

.16 

.61 

•5 

2.28 

.109 

12 

7-85 

7.17 

4.91 

4.09 

.82 

i-53 

.67 

75 

•75 

2-53 

.109 

12 

8.64 

7-95 

5-94 

5-03 

•9 

1  39 

51 

3-04 

•875 

2.66 

.109 

12 

9-03 

8-35 

6.49 

5-54 

•95 

•44 

3- 

2.78 

.109 

12 

9.42 

8.74 

7  07 

6.08 

•99 

1.27 

•37 

3-33 

3-25 

3.01 

.12 

II 

10.21 

9.46 

8  3 

7.12 

1.18 

1.17 

.26 

3-96 

3-5 

3.26 

.12 

II 

II. 

10.24 

9.62 

8-35 

1.27 

1.09 

•17 

4.28 

3-75 

3-5i 

.  12 

II 

11.78 

ii  .03 

ii  .04 

9.68 

'•37 

i  .02 

.09 

4.6 

4- 

3-73 

•134 

IO 

12.57 

ii  72 

I2-57 

10.94 

1.63 

•95 

.02 

5-47 

4-25 

3'98 

•134 

10 

13-35 

12.51 

14.19 

12.45 

t-73 

•9 

.96 

5.82 

4-5 

4-28 

10 

14.14 

13.20 

15-9 

14.07 

1.84 

•85 

•9 

6.17 

4-75 

4.48 

•134 

10 

14.92 

14.08 

17.72 

15.78 

1.94 

.8 

•85 

6.53 

5- 

4-7 

.148 

9 

15-7I 

14.78 

19.63 

17-38 

2.26 

.76 

.81 

7.58 

5-25 

4  95 

.148 

9 

16.49 

15-56 

21.65 

19.27 

2,37 

•73 

•77 

7  97 

5-5 

5-2 

.148 

9 

17.28 

16.35 

23.76 

2[.27 

2-49 

•  7 

•73 

8.36 

6. 

-l65 

8 

18.85 

17.81 

28.27 

25.25 

3-02 

.64 

•67 

10.  16 

8.' 

6'.6?7 
7.67 

.I65 
.165 

8 
8 

21.99 

20.95 
24.1 

38.48 
50.27 

34-94 
46.2 

1:3 

•55 
,48 

•S7 
•5° 

11.9 
13-65 

9- 

8.64 

.18 

7 

28.27 

27.14 

63.62 

58.63 

4-99 

.42 

•44 

16.76 

0. 

9-59 

•203 

6 

31.42 

30.M 

78.54 

72.29 

6.25 

•38 

•4 

20.99 

i. 

2. 

10.56 
"•54 

.22 
.229 

5 
4-5 

34-56 
37-7 

33-T7 
36.26 

95-03 
"3-1 

87-58 
104.63 

7-45 
8-47 

•35 
•32 

.36 
•33 

25-03 
28.46 

3- 

12.52 

•238 

4 

40.84 

39  34 

132-73 

123.19 

9-54 

.29 

•3 

32.06 

4- 

.248 

3-5 

42.42 

J53-94 

143.22 

10  71 

.27 

.28 

36. 

5- 

14^48 

259 

3 

47.12 

45-5 

176.71 

164.72 

11.99 

•25 

.26 

40-3 

6. 

*5-43 

.284 

2 

50.26 

48.48 

201.06 

187.04 

14.02 

24 

•  25 

47.11 

7- 

16.4 

•3 

I 

53-41 

5I-52 

226.98 

211.24 

iS-74 

.22 

•23 

52.89 

18. 

17-32 

•34 

O 

56-55 

54-41 

254-47 

235.61 

18.86 

.21 

.22 

63-32 

The  following  table*  gives  the  draught-areas  of  boiler-tubes 
and  flues,  which  have  been  computed  on  the  basis  of  the  thick- 
ness of  such  tubes  taken  from  the  price-lists  of  American  manu- 
facturers : 


*  American  Engineer,  1885. 


344 


THE   STEAM-BOILER. 


DRAUGHT-AREAS  OF  TUBES  AND   FLUES. 


External  diam- 
eter in  inches. 

Draught-areain 
square  inches. 

Draught-areain 
square  feet. 

Number  of 
tubes  or  flues 
=•  i  square  foot 
ofdraught-area. 

I 

•  575 

.0040 

250.0 

I* 

.968 

.0067 

149-3 

ii 

1.389 

.00964 

103.7 

if 

1.911 

-0133 

75-2 

2 

2-575 

•0179 

55-9 

at 

3-333 

.0231 

43-3 

2* 

4.083 

.0284 

35-2 

2| 

5-^27 

.0349 

28.7 

3 

6.070 

.0422 

23-7 

3i 

7.116 

.0494 

2O.  2 

3* 

8-347 

.0580 

17.2 

3* 

9.676 

.0672 

14-9 

4 

10.93 

.0759 

13-2 

4i 

14.05 

.0976 

1O.2 

5 

17-35 

.1205 

8-3 

6 

25-25 

•  1753 

5-7 

7 

34-94 

.2426 

4-i 

8 

46.20 

.3208 

3-i 

9 

58.63 

.4072 

2-5 

10 

72.23 

.5016 

2.0 

In  a  flue-return  tubular  boiler  the  area  of  flues  should  be 
about  20  per  cent,  and  the  draught-area  of  uptake  about  25  per 
cent  greater  than  the  draught-area  of  tubes.  Good  conditions 
for  combustion  and  steaming  are  realized  when  the  grate-sur- 
face is  8  times  and  the  heating-surface  about  200  to  240  times 
the  draught-area  of  tubes. 

The  location  and  arrangement  of  fire-tubes  has  an  impor- 
tant bearing  on  the  distance  by  which  they  may  be  safely 
separated.  In  locomotive  boilers,  where  they  only  check 
the  rise  of  currents  laden  with  steam  produced  by  their  own 
action,  they  may  be  set  closer  than  in  those  boilers,  as  many 
marine  boilers,  in  which  they  lie  above  a  crown-sheet  from 
which  enormous  quantities  of  steam  are  liberated,  which  steam, 
as  well  as  that  made  by  the  tubes  themselves,  must  traverse 
the  intermediate  spaces.  Where  the  circulation  is  forced  and 
rapid  the  tubes  may  also  be  crowded  more  than  where  natural 
and  sluggish.  In  locomotive  boilers,  the  tubes,  which  are  or- 
dinarily from  if  to  2  inches  in  diameter,  are  set  apart  from 


THE  DESIGN  OF   THE   STEAM-BOILER.  345 

one  third  to  one  fifth  their  diameters ;  but  the  larger  space  is 
probably  none  too  great. 

166.  The  Details  of  the  Problem,  as  coming  to  the  de- 
signer and  the  constructor  of  the  steam-boiler,  are  so  largely 
matters  determined  by  experience,  rather  than  by  any  scientific 
system  or  calculation,  that  much  thought  must  be  given  to 
their  consideration  from  the  point  of  view  of  the  practitioner 
in  engineering  and  of  the  artisan  engaged  in  building  such 
structures — from  the  boiler-maker's  side  rather  than  from  that 
of  the  man  of  science. 

The  selection  of  the  iron  or  steel  for  shell,  for  stays,  or  of 
the  rivets  ;  the  choice  of  style  of  riveting;  the  determination 
of  the  character  of  seam  and  lap  ;  the  decision  of  the  question 
whether  the  use  of  reinforced  seams  or  of  heavier  plates  is 
likely  to  prove  best  in  the  end  ;  the  choice  of  type  of  boiler 
even,  in  view  of  known  peculiarities  of  location  or  other 
conditions  :  these  must  all  be  settled  in  conference  with  the 
boiler-maker,  even  if  not  directed  absolutely  by  him.  It  sel- 
dom happens  that  the  engineer  making  the  designs  feels  com- 
petent to  act  throughout  without  consultation  with  his  lieu- 
tenants in  the  workshop. 

The  method  of  designing  in  its  details,  as  practised  in  the 
case  of  familiar  forms  of  boiler,  will  be  given  in  the  next 
chapter. 


CHAPTER   VIII. 

DESIGNING   STEAM-BOILERS — PROBLEMS   IN   DESIGN. 

167.  The  General  Considerations  determining  the  design 
of  a  steam-boiler  are,  mainly,  the  following : 

(1)  It  must  supply  a  defined  quantity  of  steam  in  a  speci- 
fied unit  of  time,  or  it  must  have  a  certain  power. 

(2)  It  must  be   as   absolutely  safe   as  it  is  practicable  to 
make  it. 

(3)  It  must  have  reasonably  high  efficiency,  and  must  be 
capable  of  working  at  the  lowest  total  expense  for  fuel,  attend- 
ance, interest  on  first  cost,  taxes,  insurance,  and  all  other  run- 
ning expenses,  in  proportion  to  work  done,  that  may  be  attain- 
able. 

(4)  It  must  be  well  suited  to  the  location,  and  to  all  the 
special  conditions  affecting  it  when  in  operation. 

Marine  steam-boilers  must,  for  example,  be  given  the  mini- 
mum practicable  weight  and  volume,  since  it  costs  as  much  to 
carry  a  ton  of  boiler  as  a  ton  of  cargo,  and  every  cubic  foot 
occupied  by  boilers,  fuel,  or  machinery  displaces  a  cubic  foot  of 
paying  load.  Naval  boilers,  also,  must  usually  be  kept  as  low 
in  the  ship  as  possible  to  reduce  risk  of  injury  by  shot.  So 
important  are  these  elements  in  naval  construction,  that  the 
practical  limits  of  space  and  power  on  shipboard  are  com- 
monly fixed  by  the  space  occupied  by  boilers ;  and  the  reduc- 
tion of  grate-area  is  the  first  problem  attacked  by  the  naval 
architect  and  engineer  seeking  high  speed,  whether  for  yachts, 
torpedo-boats,  or  larger  craft. 

168.  The  Parts  and  Details  of  the  steam-boiler  may  be 
defined  as  follows  :* 

*  See  Rankine,  Steam-engine,  p.  449. 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    347 

The  usual  arrangements  of  furnace  and  boiler  may  be 
divided  into  three  principal  classes : 

(I.)  In  the  external  furnace,  or  "  outside-fired  boiler/'  the 
furnace  is  wholly  outside  of  the  boiler ;  so  that  the  boiler 
forms  part  of  the  superficies  of  the  furnace;  the  other  sides  of 
the  furnace  being  usually  of  fire-brick.  Examples  of  this  are 
the  wagon  boiler,  the  plain  cylindrical  boiler  without  internal 
flues,  and  all  boilers  in  which  the  water  and  steam  are  con- 
tained in  tubes  surrounded  by  the  flame. 

(II.)  In  the  internal-furnace  or  "  inside-fired  boiler"  the 
fire-chamber  is  enclosed  within  the  boiler,  as  in  boilers  with 
furnaces  contained  in  horizontal  cylindrical  internal  flues,  in 
most  marine  boilers,  and  in  all  locomotive  boilers. 

(III.)  The  detached  furnace,  which  is  a  fire-chamber  built 
of  fire-brick,  in  which  the  combustion  is  completed  before  the 
gas  comes  in  contact  with  the  boiler. 

The  principal  parts  and  appendages  of  a  furnace  are — 

(1)  The  furnace  proper,  or  firebox,  being  the  chamber  in 
which  the  solid  constituents  of  the  fuel,  and  the  whole  or  a 
part  of  its  gaseous  constituents,  are  consumed. 

(2)  The  grate,  which  is   composed  of   alternate   bars  and 
spaces,  to  support  the  fuel  and  to  admit  air. 

(3)  The  hearth  is  a  floor  of  fire-brick,  on  which,  instead  of 
on  a  grate,  the  fuel  is  burned  in  some  furnaces. 

(4)  The  dead-plate  or  dumb-plate,  that  part  of  the  bottom 
of  the  furnace  which  consists  of  an  iron  plate  simply. 

(5)  The  mouth-piece,  through  which  fuel  is  introduced,  and 
often  some  air.     The  lower  side  of  the  mouth-piece  is  the  dead- 
plate.     In  many  furnaces  there  is  no  mouth-piece. 

(6)  The  fire-door  closes  the  doorway,  and  may  or  may  not 
have  openings  and  valves  in  it  to  admit  air.     Sometimes  the 
duty  of  a  fire-door  is   performed  by  a  heap  of  fuel  closing  up 
the  mouth  of  the  furnace. 

(7)  The  furnace-front  is  above   and  on  either  side  of  the 
fire-door. 

(8)  The  ash-pit  is  the  space  into  which  the  ashes  fall,  and 
through  which,  in  most  cases,  the  supply  of  air  enters. 

(9)  The  ash-pit  door  is  used  to  regulate  the  admission  of  air. 


THE   STEAM-BOILER. 

(10)  The  bridge  is  a  low  wall  at  the  end  of  the  furnace  over 
which  the  flame  passes  to  the  chimney.     This  is  meant  when 
"  the  bridge"  is  spoken  of  ordinarily;  but  the  word  bridge,  or 
bridge-wall,  is  also  applied  to  any  partition  having  a  passage 
for  flame  or  hot  gas  over  it.     Bridges  are   of  fire-brick,  or  of 
plate  iron   and  hollow,  so  as  to   form  part  of  the  water-space 
of  the  boiler,  and  are  then  called  water-bridges.     The  top   of 
a  water-bridge  should  slope  upwards  at  the  ends  to  allow  of 
the    rapid    escape    of   the    steam    on    its    internal   surface.     A 
water-bridge   may  project   downwards   from  the  boiler  above 
the  furnace  ;  it  is  then  called  a  hanging  bridge. 

(11)  The  combustion  or  flame-chamber  is   the  space  behind 
the  bridge   in  which  the   combustion  of   the  furnace-gases    is 
completed.     It  may  be  lined  with  brick  or  tile  to  prevent  ex- 
tinction of  the  flame. 

(12)  Bafflers  or  diffusers  are  partitions  so  placed  as  to  pro- 
mote the  circulation  of  the  gas  over  the  heating  surface  of  the 
boiler  or  of  the  currents  of  water  within.     Bridges  fall  under 
this  head. 

(13)  Dampers  are  valves  placed   in  the  chimney,   flues,  or 
passages  to  regulate  the  draught. 

The  principal  parts  and  appendages  of  a  body  are  : 

(1)  The  shell  of  the  boiler.     The  figures  usually  employed 
for  the  shells  of  boilers  are  the  cylindrical  and  the  plane,  and 
combinations    of    those    two    figures.     In   locomotive  boilers, 
part  of  the  shell  is  a  rectangular  box,  containing  within  it  the 
firebox.      The  shells  of  marine  boilers  are   often  of  irregular 
shapes,   adapted  to  the  space  in   the   ship  which  they  are  to 
occupy,  and  approximating  more  or  less  to  rectangular  forms. 
For  heavy  pressures,  however,  they  are  usually  cylindrical,  with 
plane  ends. 

(2)  The   steam-chest,  steam-drum,  or  dome  is  a  part  which 
rises   above   the  rest  of    the  boiler,   and  provides  a   space    in 
which  the  steam  may  deposit  any  spray  carried   by  it ;  it   is 
usually  cylindrical. 

(3)  The  furnace  or  firebox  is  usually  within  the  boiler,  so 
placed  as  to  be  covered  with  water.     In  cylindrical  boilers  it  is 
often  in  one  end  of  a  horizontal  cylindrical  flue,  as  in  Cornish 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    349 

boilers ;  in  locomotive  boilers  it  is  a  rectangular  box.  In 
marine  boilers  it  is  usually  rectangular  in  the  older  kinds  of 
boiler,  and  cylindrical  in  the  high-pressure  cylindrical  tubular 
boiler. 

(4)  A  tube-plate  forms  part  of  the  shell  of  the  boiler,  or  one 
side  of   an   internal    firebox,   or   flue,   and   is   perforated   with 
holes,  into  which  the  ends  of  the  tubes  are  fixed.      Each  set 
requires  a  pair,  one  for  each  end  of  the  tubes. 

(5)  The  man-hole  is  an  opening  in  the  top  or  end  of  the 
boiler,  large  enough  to  admit   a  man.     The  bolts  holding  the 
man-hole  cover  must  be  capable  of  safely  bearing  their  load. 
Commonly  the  cover  opens  inwards,  and  is  kept  closed  by  the 
pressure  of  the  steam,  and  is  held  by  bolts  and  nuts  to  a  cross- 
bar outside  the  man-hole. 

(6)  Hand-holes  are  openings  usually  placed  at  or  near  the 
lowest  part  of  a  boiler,  and  large  enough  to  admit  the  hand, 
which  are  opened  occasionally  for  the  discharge  of  sediment. 

(7)  The  blow-off  apparatus  consists  of  a  cock  at  the  bottom 
of  the  boiler,  which  is  opened  to  cleanse  the  boiler  by  empty- 
ing it  or  to  discharge  brine,  and   prevent  salt   from  collecting. 
The  surface  blow-cock  discharges  the  scum  which   collects  on 
the  surface  of  the  water. 

(8)  The   pressure-gauge    shows    the    pressure    within    the 
boiler. 

(9)  The  water-gauge  shows  the  level   of   the  water  in  the 
boiler.     Gauge-cocks  are  set   at    different    levels :    one  at    the 
proper  water-level,  another  a  few  inches  above,  and  a  third  a 
few  inches  below.     Opening  these  the  engineer  ascertains  the 
level  of  the  water.     The  glass  water-gauge  consists  of  a  strong 
glass   tube,  communicating  with   the  boiler  above  and  below 
the  water-level.     The  level  of  the  water  is  thus  rendered  visi- 
ble.    Every  boiler  ought  to  be  provided  with   both  forms  of 
gauge. 

(10)  Clothing  and    lagging   prevent  waste    of   heat.      The 
former  is  made  sometimes  of  hair  felt,  the  latter  covers   it  with 
a  layer  of  thin  wooden  boards.     Asbestus,  ashes,  and  other  ma- 
terials are  similarly  used.      Hair-felt  has  sometimes  been  found 
to  singularly  accelerate  internal  corrosion. 


350  THE   STEAM-BOILER. 

169.  The  Design  of  the  Plain  Cylindrical  Boiler  is  the 

simplest  problem  of  its  class.  This  boiler,  consisting  of  only 
a  cylindrical  shell  and  plane  or  domed  heads,  is  not  likely  to 
afford  opportunity  for  the  display  of  either  great  knowledge  in 
design  and  construction  or  of  ingenuity  in  its  details.  This 
type  is  selected  when  cheap  fuel  or  bad  water  make  it  unwise 
to  adopt  more  economical  forms. 

The  shell  is  usually  about  twelve  diameters  in  length,  but  is 
sometimes  made  fifteen  or  even  twenty,  and  double  the  last  fig- 
ure has  been  known.  In  some  cases  this  boiler  has  been  built  as 
a  cylindrical  ring — an  annulus  of  large  diameter  and  of  circular 
section.  Common  sizes  for  this  class  of  boiler  range  from  24 
to  36  inches  (63  to  91  cm.)  diameter  of  shell,  and  24  to  36  feet 
(7.3  to  1 1  m.)  long.  As  the  diameter  of  the  boiler  usually  fixes 
the  width  of  grate,  and  as  the  length  of  grate  is  rarely  found  to 
be  profitably  extended  beyond  about  6  feet  (1.8  m.),  the  power 
of  the  boiler  has  a  very  simple  relation  to  its  size.  The  ratio 
of  heating  to  grate  surface  is  always  thus  made  small,  and  the 
boiler  is  necessarily  uneconomical  of  fuel. 

This  boiler  is  usually  designed  with  single-riveted  seams 
throughout,  although  safety  and  even  ultimate  economy  of 
cost  and  operation  during  its  lifetime  may  be  sometimes  gained 
by  double-riveting  the  longitudinal  seams  ;  which  would  thus 
be  strengthened  in  the  proportion  of  about  70  to  55  or  60,  01 
not  far  from  20  per  cent,  and  the  whole  structure  would  be 
made  correspondingly  safer. 

The  thickness  of  shell  is  determined  by  the  pressure  of 
steam  to  be  carried  and  the  factor  of  safety  adopted.  Assum- 
ing the  iron  to  have  a  tenacity  of  50,000  pounds  per  square 
inch  (3515  kilogs.  per  sq.  cm.),  the  joints  will  have,  as  may  be 
assumed,  0.60  this  resisting  power,  and  the  boiler-shell  is  to  be 
calculated  with  this  loss  in  mind,  and  will  be  made  as  if  the 
sheets  had  a  tenacity  of  30,000  pounds  per  square  inch  (2109 
kgs.  per  sq.  in.),  and  were  of  uniform  strength  through  the 
seams.  In  illustration,  assume  it  to  be  demanded  that  a  "  36- 
inch  cylindrical  boiler"  shall  be  designed  to  sustain  a  pressure 
of  100  pounds  per  square  inch  (7  kilogs.  per  sq.  cm.).  The 
thickness  of  shell  should  be. 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    35 1 

t  __  fPd '  =     6  X  IPO  X  36       _o 
~  2kT~  2  X  0.55  X  50,000  ~~  * 

when  /,  d,  and  T  are  the  pressure  and  the  diameter  of  the 
shell  and  the  tenacity  of  the  metal,  and  k  is  the  "  efficiency"  of 
the  seam,  which  we  may  here  assume  to  have  k  =  0.55,  or  55 
per  cent  of  the  strength  of  the  solid  sheet ;  the  factor  of  safety 
is  taken  as/— 6.  The  thickness  of  shell  should  be  three- 
eighths  of  an  inch  (i  cm.  nearly).  Such  thickness  is  not  usual, 
and  a  factor  of  safety  of  four  and  a  thickness  of  one  quarter  of 
an  inch  (0.635  cm.)  is  more  common  for  this  case  in  general 
practice,  and  is  allowed  by  the  law  as  may  be  seen  in  article 
55,  to  which  reference  may  be  made  for  tabulated  legal  dimen- 
sions of  this  class  of  boilers. 

The  heads  of  the  cylindrical  boiler  are  sometimes  made  of 
cast-iron,  the  thickness  made  empirically  from  i£  to  2|-  inches 
(3.8  to  6.4  cm.)  for  diameters  of  from  24  to  36  inches  (63  to  91 
cm.)  respectively  ;  they  are  often  of  sheet-iron  of  the  same 
thickness  as  the  shell,  and  domed  to  give  them  resisting  power, 
— an  excellent  construction,  especially  when  pressed  into  exact 
shape  in  the  forming  die  of  the  hydraulic  press.  When  the 
heads  are  plane,  they  are  stayed  either  by  stays  running  to  the 
sides  of  the  boiler  at  angles  of  from  10°  to  30°,  or  by  triangu- 
lar "gusset-plates"  riveted  to  the  heads  and  sides.  This  last 
construction  is  subject  to  the  objection  that  the  gusset-plates 
are  necessarily  irregularly  strained  and  liable  to  tear.  Stay- 
rods  are  of  sufficient  size  to  safely  carry  the  whole  pressure  re- 
ceived on  the  heads,  and  securing  both  heads,  pass  from  the 
one  to  the  other,  the  whole  length  of  the  boiler,  with  adjust- 
able nuts  at  each  end,  outside  the  head,  and  inside  as  well. 

A  dished  head  is  probably  the  best  form  to  give,  whether  of 
boiler,  of  dome,  or  of  steam  and  mud  drums.  As  shown  by 
Mr.  Robert  Briggs,*  equal  strength  with  the  shell  or  with  a 
stayed  head  can  be  obtained  by  giving  the  proper  form  to  the 
head-sheet  without  any  staying.  Thus  it  is  known  that  the 
strength  of  a  spherical  shell  is  twice  as  great  as  that  of  the 

*  Journal  Franklin  Institute,  1878. 


352  THE   STEAM-BOILER. 

cylinder  of  the  same  diameter,  when  both  shell  and  cylinder 
have  the  same  thickness ;  or  that  a  spherical  shell  possesses 
the  same  strength  as  a  cylindrical  shell  of  the  same  thickness, 
when  the  radius  of  the  spherical  surface  is  equal  to  the  diame- 
ter of  the  cylinder.  When  the  rule  stated  is  applied  to  the 
head  of  the  dome  or  of  the  boiler,  which  is  formed  to  a  part  of 
a  spherical  surface  whose  radius  is  the  diameter  of  the  dome  or 
boiler,  the  head  is  "dished"  out  0.134  the  diameter  of  the 
head,  in  order  to  give  the  same  strength  to  resist  internal  pres- 
sure, for  both  head  and  shell,  of  the  same  thickness  of  iron.  A 
small  allowance  is  needed  for  the  thinning  of  the  sheet-iron,  in 
dishing.  This  allowance  is  easily  computed  thus :  The  sur- 
face of  the  flat  circular  plate  is  to  that  of  the  dished  plate  as 
I  to  1.072,  and  the  thickness  of  the  circle,  before  dishing,  should 
be  about  7  per  cent  (one  fourteenth)  greater  than  that  of  the 
shell.  The  flangeing  of  the  head  will  inevitably  upset  the  flange 
itself  to  a  thickness  much  above  the  original ;  and  a  dished  head 
of  ordinary  thickness  will  be  much  stronger  than  the  shell 
sheets  at  the  joints,  where  they  are  weakened  by  rivet-holes, 
even  if  put  together  with  the  double-riveted  longitudinal 
seams. 

Heads  of  sheet-iron  are  usually  made  ten  or,  better,  twenty 
per  cent  heavier  than  the  shell. 

A  man-hole  is  commonly  located  in  the  most  accessible  end 
of  the  boiler,  and,  often,  a  hand-hole  through  which  the  boiler 
may  be  completely  drained,  and  all  mud  and  scale  removed. 
The  feed-pipe  usually  enters  through  the  front  head,  but  some- 
times at  the  rear.  It  should  always  be  at  a  part  readily  reached 
for  inspection  and  repairs.  If  on  the  shell,  the  opening  should 
always  be  reinforced  by  a  heavy  wrought-iron  ring  and  the 
strength  of  the  boiler  thus  increased  rather  than  diminished  by 
its  introduction.  The  ring  should  be  riveted  inside  the  open- 
ing. The  steam-pipe  is  sometimes  led  directly  out  of  the  top 
of  the  boiler,  but  is  better  placed  in  connection  with  a  steam- 
dome  or  steam-drum,  in  order  to  obtain  as  dry  steam  as  is  pos- 
sible. The  safety-valve  should  here,  as  in  all  other  cases,  be  so 
placed  that  no  accident  or  carelessness  can  close  its  communi- 
cation with  the  steam-space ;  a  stop-valve  placed  between  it 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    353 

and  the  boiler  has  been  known  to  produce  a  disastrous  explo- 
sion, when  shut  by  an  ignorant  or  thoughtless  attendant. 

Gauge-cocks  should  always  be  attached  even  if  the  glass 
water-gauge  is  in  use.  The  experienced  manager  of  boilers 
never  feels  perfect  confidence  in  any  other  water-level  indicator, 
however  convenient  and  generally  accurate.  In  setting  the 
gauge-cocks  it  is  usual  to  allow  about  one  third  the  volume 
of  the  boiler  for  steam-space.  The  following  table,  calculated 
by  Mr.  W.  F.  Worthington,  gives  the  volume  of  this  space  in 
unity  of  length  of  the  shell,  British  measures : 


TABLE   FOR   CALCULATING  THE   CAPACITY   OF  THE   STEAM  -  SPACE  IN" 
CYLINDRICAL    BOILERS. 


DlAM 

30  • 

32" 

34" 

36" 

38. 

40  » 

42  » 

48, 

54" 

60  » 

66  . 

721 

In. 

Multipliers  (cubic  feet). 

In. 

'&  * 

•05 

•05 

•05 

•05 

.05 

.06 

.06 

.06 

.06 

.07 

.07 

.08 

i 

£        2 

•  14 

.14 

•  *S 

•15 

.16 

.16 

.l6 

•  17 

.'9 

.20 

.21 

.  2  1 

2 

J      3 

•  25 

.26 

•27 

.28 

.29 

•3° 

•3° 

•32 

•34 

•37 

.38 

•39 

3- 

v-      4 

•39 

.40 

.42 

•43 

•44 

•45 

.46 

•  50 

•53 

•55 

-58 

.61 

4 

c      5 

•53 

•56 

•57 

•59 

.61 

•63 

.64 

.69 

•73 

.78 

.82 

•85 

5- 

c     6 

.70 

•72 

•75 

•77 

.80 

.82 

•83 

.91 

.90 

i  .02 

1.  08 

.  12 

6 

w      7 

.87 

.90 

•93 

.96 

•99 

.02 

1.05 

1.14 

i  .  20 

1.27 

'•35 

•41 

7 

w     8 

•05 

.09 

•13 

1.17 

1.20 

.24 

1.27 

i-37 

1-47 

i  -55 

1.63 

•71 

8    £ 

v     9 

.24 

.29 

•33 

1.38 

1.42 

•47 

i-5i 

1.62 

i-73 

1.85 

1.94 

.04 

~y 

J3     I0 

•43 

•49 

•55 

1.65 

.70 

i-75 

1.89 

2.02 

2.14 

2.26 

.38 

10     0 

7,     II 

.63 

69 

.76 

1.82 

1.89 

95 

2.OO 

2.18 

2-33 

2.46 

2-59 

•74 

ii  :l 

S       2 

•83 

.91 

.98 

2.06 

2.13 

2.20 

2.26 

2.46 

2    63 

2-79 

2-95 

3.08 

12      C 

>     3 

2.04 

2    13 

2.21 

2.30 

2.  "8 

2.46 

2-53 

2-75 

2-93 

3-12 

3-3i 

3.46 

i-    a. 

I     4 

2.24 

2  35 

2-44 

2  -53 

2.63 

2    72 

2.80 

3-°4 

3  25 

3-47 

3-67 

3-85 

14  3- 

1      5 

2-57 

2.68 

2-79 

2.89 

2.98 

3.08 

3-6< 

3-84 

4-05 

4.26 

X5    £ 

«£         6 

2.92 

3-°3 

3-<5 

3.26 

3-37 

3.66 

3-94 

4.19 

4-43 

4-67 

16    „ 

u      7 

3.28 

3.41 

3-65 

3  98 

4  29 

4-57 

4-83 

5-09 

17  -5 

e     8 

3.67 

3.8l 

3-93 

4-30 

•4-6j 

4-95 

5-23 

5-53 

18  •£ 

3      9 

4.08 

4.22 

4-63 

5.00 

5^2 

5-66 

5-97 

19   ii 

.2   20 

4-52 

4.96 

5-35 

5-72 

6  08 

6.41 

20  *; 

C     21 

5.28 

5-72 

6.12 

6.50 

6.84 

21     * 

5-6i 

6.10 

6.51 

6.92 

7-3° 

22     f 

5  95 

6.46 

6.92 

7-35 

7.76 

23    I' 

6.82 

7-33 

7-79 

8.24     !     24      v 

7.20 

7-75 

8.22 

8.71  !  25  g 

7-57 

8.15 

8.70 

9.20       26    ctf: 

RULE.—  Multiply  the  number  in  the  table  by  the 
length  of  the  boiler  in  feet,  and  the  product  will  be 
the  capacity  of  the  steam-space  in  cnbic-feet. 

8-57 
8.97 
9-39 

9.14 

9-59 
10.04 
10.49 

9.68      27  .<n: 
0.17      28  Qi 

0.67       29 
1.  1  6      30 

10.94 

1.62      31 

"•39 

2.12          32 

2.62      33 

13-12      34 

13-63      35 

In  designing  this,  as  any  other  boiler  having  a  cylindrical 
shell  and   fired  externally,  it  is   advisable   to  secure  as  large 
23 


354  THE    STEAM-BOILER. 

sheets,  and  as  few  seams  on  the  under  side  and  where  exposed 
to  the  action  of  the  fire  and  the  furnace  gases,  as  possible. 
Boilers  are  now  often  made  with  but  a  single  sheet  extending 
from  end  to  end,  and  of  such  width  that  all  longitudinal  seams 
are  above  the  reach  of  flame. 

The  steam-space  should  be  of  such  volume  that  the  varia- 
tion of  pressure  produced  by  each  stroke  of  the  engine  should 
be  unimportant.  An  old  rule  given  by  Bourne  made  the  space 
not  less  than  twelve  times  the  volume  of  steam  taken  out  by 
the  engine  at.  each  stroke  ;  it  may,  however,  be  less  for  a  given 
power  as  the  speed  of  rotation  of  the  engine  is  higher  and  as 
the  ratio  of  expansion  is  increased.  Tredgold  would  restrict 
the  variation  of  steam-pressure  at  each  stroke  to  about  three 
per  cent  of  the  normal  amount,  which  would,  if  V  be  the 
volume  of  steam-space  of  the  boiler,  .5  that  of  the  single  cylin- 
der, up  to  the  point  of  "  cut-off,"  and  r  the  ratio  of  expansion, 
adopting  Tredgold's  coefficient,  0.033, 


For  coupled  engines,  a  much  smaller  space  may  be  al- 
lowed. 

According  to  Shock,*  marine  boilers  of  the  older  types 
work  dry  when  they  contain  in  their  steam-space  a  supply  suf- 
ficient for  the  engine  during  14  seconds  and  give  wret  steam  if 
the  steam-space  is  sufficient  for  but  12  seconds  ;  while  the  more 
modern  forms  of  high-pressure  boilers  will  only  furnish  dry 
steam  when  containing  a  volume  equal  to  20  seconds'  supply. 
Steam-space  of  considerable  altitude  is  most  effective. 

170.  Stationary  Flue-boilers  are  designed,  as  to  dimen- 
sions of  shell,  very  much  as  are  plain  cylindrical  boilers. 
They  are  commonly  of  somewhat  larger  diameter  and  of  com- 
paratively less  length. 

The  Cornish  boiler,  in  which  the  single  great  flue  serves  also 
as  furnace,  is  rarely  made  of  less  than  6  feet  (1.8  m.)  in  diame- 
ter, as  a  smaller  flue  than  that  so  obtained  gives  too  contracted 


*  Steam-boilers,  p.   306. 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    355 

a  furnace.  The  length  of  this  boiler  is  usually  from  25  to  40 
feet  (7.6  to  12  m.).  The  thickness  of  shell  is  made  about  \  inch 
(1.27  cm.)  and  of  flue  f  inch  (0.95  cm.)  for  the  shorter  and  J 
inch  (1.27  cm.)  for  the  greater  length,  the  steam-pressure 
adopted  being  usually  about  40  pounds  per  square  inch  (3  at.). 
Both  should,  however,  be  carefully  computed  by  the  methods 
already  given  (§§  55,  56),  and  a  good  factor  of  safety — not  less 
than  6 — is  advised  to  be  adopted  and  permanently  maintained. 
The  flue  is  nearly  always  one  half  the  diameter  of  the  shell. 
Where  the  boiler  is  long,  and  the  flue  thus  becomes  structurally 
weak,  strengthening  rings,  or  flanged  girth-seams,  should  be 
adopted  to  insure  greater  strength  and  safety  in  the  flue,  which 
should,  because  of  its  special  liability  to  injury  and  general,  as 
distinguished  from  local,  failure,  be  even  safer  against  collapse 
than  the  shell  against  bursting.  Collapse  of  the  flue,  however, 
is  less  likely  to  be  disastrous  to  life  and  surrounding  property 
than  explosion  of  the  shell.  The  heads  are  so  well  stayed  by 
the  flue  that  they  require  no  other  bracing  below  the  water- 
line  ;  above  that  level,  however,  they  should  be  stayed  by  ei- 
ther stay-rods  or  gusset-pieces,  like  the  plain  cylindrical  boiler. 
The  same  remarks  also  here  apply,  relative  to  appurtenances  of 
the  boiler,  as  in  the  preceding  case. 

Multifluf  Boilers  are  constructed  either  with  or  without 
fireboxes.  The  latter  will  be  considered  more  at  length  in 
later  articles.  Flue-boilers  without  fireboxes  are  simply  com- 
posed of  a  cylindrical  shell  with  plane  heads,  and  having  flues 
running  from  end  to  end,  below  the  water-line,  and  secured  in 
the  heads,  at  each  end,  by  means  of  flanges  turned  in  those 
41  flue-sheets"  and  riveted  to  the  ends  of  the  flues.  These 
flanges  are  usually  turned  inwards,  but  are  sometimes  on  the 
exterior,  the  projecting  end  of  the  flue,  extending  beyond  the 
plane  of  the  head.  The  number  and  size  of  these  flues  is  de- 
termined mainly  by  the  judgment  of  the  designer,  and  no  rule 
exists ;  but  the  better  the  water  used  and  the  more  valuable 
the  fuel  consumed,  the  more  numerous  the  flues.  Where  two 
are  put  in,  they  are  commonly  about  one  third  the  diameter  of 
the  boiler,  each,  and  are  set  side  by  side  below  the  horizontal 
•diametral  line  of  the  shell.  When  more  are  used,  the  number 


356 


THE    STEAM-BOILER. 


is  first  increased  to  five,  each  of  about  one  fourth  the  size  of 
the  boiler-shell.  With  still  further  subdivision  the  designer 
puts  them  in  as  he  best  can,  ordinarily  keeping  their  centres  at 
the  intersections  of  horizontal  and  vertical  lines,  set  apar'  dis- 
tances equal  to  the  diameter  of  flue  plus  the  desired  space  for 
circulation,  which  varies  from  one  half  to  one  fourth  the  diam- 
eter of  the  flue  accordingly  as  the  latter  are  more  or  less  nu- 
merous. Ample  room  for  circulating  currents  is  no  less  essen- 
tial to  efficiency  than  extent  of  heating-surface,  and,  as  a  matter 
of  safety,  more  so.  Small  flues  are  commonly  made  of  iron  of 
the  same,  or  somewhat  less,  thickness  with  the  shell,  and,  when 
numerous,  have  an  excess  of  strength  over  that  indicated  by 
calculation  and  a  correspondingly  increased  margin  for  safety. 


FIG.  74. — FLUE  \VITH  RINGS. 


Flues  of  sizes  below  5  or  6  inches  (1.5  or  1.8  cm.)  diam- 
eter are  not  usually  riveted  up,  as  is  the  case  with  the  larger 
flues,  but  are  commonly  drawn  in  the  tube-rolling  mill  and  are 
known  in  the  market  as  tubes.  The  larger  mills  also  often  pro- 
duce drawn  tubes,  or  flues,  of  much  larger  size ;  some,  handled 
by  the  Author,  have  been  as  large  as  16  inches  (4.9  cm.). 
In  consequence,  partly,  of  such  changes  in  modern  facilities  for 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    357 

construction,  and  for  various  other  obvious  reasons,  the  tubu- 
lar has  very  generally  superseded  the  flue  boiler.  Where  still 
used,  it  is  customary  to  allow  about  12  square  feet  (1.16 
sq.  m.)  of  heating  surface  per  horse-power,  and  not  far  from 
20  to  I  as  the  proportion  to  grate-surface. 

Fig.  74  illustrates  a  case  in  which  the  flues  are  strength- 
ened by  rings,  placed  at  the  girth-seams  joining  each  adjacent 
pair  of  ring-courses. 

The  domestic  make  of  corrugated  flue  now  used  in  the 
"  Scotch"  marine  boiler  is  illustrated  in  the  following  engraving. 


FIG.  75.— THE  CORRUGATED  FLUK. 


In  this  class  of  boiler   it  proves    particularly  valuable,  since 
the  construction  here  met  with,  of    high  steam-pressure  and 


FIG.  76. — FORM  OF  CORRUGATED  FLUE  USED  AS  FURNACE  IN  MARINE  BOILER. 

a  forced  fire,  is  one  which  demands  strength  of  structure,  and, 
at  the  same  time,  compels  the  use  of  thin  iron.     One  objection 


THE   STEAM-BOILER. 

to  this  form  of  flue  is  found  in  its  liability  to  become  encrust- 
ed with  scale  or  with  sediment  in  the  corrugations. 

Fig.  76  shows  the  form  given  the  corrugated  flue  when 
constructed  for  use  as  a  furnace  in  a  marine  boiler,  and  as 
made  by  Mr.  Fox,  who  first  successfully  manufactured  them. 
The  joints  are  welded  in  a  gas-flame,  and  are  usually  but  little, 
if  at  all,  weaker  than  the  solid  sheet. 

For  good  stationary  boilers,  according  to  Cave,*  about  4 
pounds  of  steam  may  be  allowed  as  the  evaporation  to  be  ex- 
pected per  square  foot  of  heating  surface  (19  kgs.  per  sq.  m.)  ; 
but  this  quantity  is  very  variable  with  the  form  and  proportions 
of  the  boiler,  locomotive  boilers  producing  several  times  this 
quantity,  and  the  amount  so  evaporated  increasing  generally 
as  the  efficiency  of  the  generator  diminishes.  The  Cornish 
boiler,  as  formerly  customarily  operated,  supplied  but  about  one 
fourth  the  above-mentioned  quantity  of  steam. 

171.  The  Cylindrical  Tubular  or  Multitubular  boiler  like 
the  flue  boiler,  may  be  made  either  with  or  without  firebox ; 
it  is  now  most  frequently  made  "  plain,"  consisting  of  a  cylin- 
drical shell,  with  plane  heads  and  a  "  nest "  of  tubes  fitting  and 
nearly  filling  the  water-space  up  to  the  water-level.  The  com- 
mercial and  accepted  rating  and  proportions  of  this  class  of 
steam-boiler  have  already  been  given  in  §  161.  In  all  impor- 
tant work,  the  designing  engineer  will  carefully  determine  the 
size  and  economical  proportions  for  the  special  case  in  hand. 
The  following  may  be  taken  as  illustrating  the  process  for  this 
case,  as  well  as  for  boilers  generally : 

It  is  required  to  design  a  tubular  boiler  or  a  set  of  boilers 
capable  of  supplying  steam  to  a  condensing  engine  of  500  horse- 
power, guaranteed  to  demand  not  more  than  22  pounds  (10 
kgs.)  of  steam  per  H.  P.  per  hour,  the  pressure  to  be  100  pounds 
per  square  inch  (6%  atmospheres),  and  the  feed-water  to  be 
taken  from  the  condenser  at  120°.  Fahr.  (48°.  8  C). 

The  first  step  is  to  determine  the  quantity  of  steam  to  be 
made.  Calculation  on  the  above  basis  would  make  it  11,000 
pounds  (4990  kgs.)  per  hour,  evaporated  from  120°  Fahr.  (48°. 8 

*  Traite  des  Machines  a  Vapeur;  Bataille  et  Jullin. 


DESIGNING   STEAM-BOILERS— PROBLEMS  IN  DESIGN.    359 

C.)  at  338°  Fahr.  (170°  Cent.)  as  shown  by  the  steam-tables 
(Appendix,  Table  I.).  At  the  customary  rating,  however  (30 
pounds  or  13.6  kgs.  per  horse-power),  the  weight  to  be  evapo- 
rated would  be  15,000  pounds  (6804  kgs.)  per  hour,  and  this 
larger  figure  is  taken  as  permitting  a  good  margin.  Were  this 
evaporated  by  the  best  fuel  and  in  a  boiler  having  the  efficiency 
unity,  it  would  require  the  supply  of  1000  pounds  (4536  kilogs) 
of  coal  per  hour. 

The  financially  desirable  efficiency  of  the  boiler  should  be 
next  determined  as  indicated  in  the  chapter  devoted  to  that 
subject ;  it  may  be  here  assumed  to  have  been  found  to  be 
0.75  ;  and  1333  pounds  (6048  kgs.)  of  fuel  would  be  demanded 
per  hour.  By  the  use  of  the  expression  already  found  (§  98) 
we  have 


in  which  we  may  take  A  —  0.5  and  B  —  i  ;  then 


0.5         2 
and 

S=2F.      .      .      .      .....      (2) 

Thus  the  best  ratio  of  heating  to  grate  surface  is  twice  the 
number  representing  in  British  measures  the  quantity  of  fuel 
burned  on  the  unit  area  of  grate.  It  thus  becomes  necessary 
as  a  next  step  to  ascertain  this  last  quantity,  and  therefore  to 
ascertain  the  height  of  chimney.  This  is,  in  the  case  of  con- 
siderable power,  as  here,  to  be  determined  by  the  principles  de- 
tailed in  §§  157  and  158.  A  height  of  125  feet  may  be 
taken  as  the  result  of  this  investigation.  A  well-designed 
chimney  of  this  altitude  should  permit  the  combustion  of  15 
pounds  per  square  foot  (7.5  kgs.  per  sq.  m.)  of  grate  with  a  mar- 
gin of  at  least  one  third  for  contingencies.  On  this  basis,  the 


360 


THE   STEAM-BOILER. 


area  of  grate  must  be  82  square  feet  (7.6  sq.  m.)  and  the  area 
of  heating  surface  2460  square  feet  (228  sq.  m.  nearly).  This 
is  to  be  distributed  among  two  or  more  boilers ;  since,  although 
a  thousand  horse-power,  even,  may  be,  and  sometimes  is,  ob- 
tained from  a  single  boiler,  it  is  usually  found  inexpedient  to 
concentrate  power  to  such  an  extent. 

A  boiler  of  5  feet  (1.5  m.)  diameter  and  2\  or  3  diameters 
long  has  become  a  very  common  and  very  satisfactory  size. 
This  permits  a  grate  of  about  30  square  feet  (2.8  sq.  m.),  and 
three  such  boilers  having  grates  6  feet  (1.8  m.)  in  length  would 
give  the  required  grate-area  with  an  allowance  of  ten  per  cent 


FIG.  77.— TUBULAR  BOILER. 

for  ineffective  surface  along  the  edges  and  in  the  corners.  H 
may  be  taken  as  a  good  rule  to  throw  in  all  such  differences 
on  the  side  of  increased  boiler-power.  A  boiler  of  this  charac- 
ter with  3-inch  (7.6  cm.)  diameter  of  tube  will  be  found  to  have 
63  square  feet  (5.9  sq.  m.)  area  of  heating-surface  per  unit 
length,  and  a  length  of  15  feet  (4.57  m.)  gives  very  exactly  the 
desired  total  area  for  a  single  boiler.  The  proportion  of  length 
of  tube  to  diameter,  60  to  I,  is  considered  a  good  one,  although 
rather  high  ;  and  such  a  boiler  operated  under  the  assumed  con- 
ditions would  supply  the  power  demanded  with  the  intended 
economy  of  fuel. 


DESIGNING   STEAM-BOILERS— PROBLEMS  IN  DESIGN.    361 

The  tube- sheets  would  be  made,  if  of  steel,  a  half-inch  (1.27 
cm.),  or  a  little  less,  in  thickness,  to  give  good  holding  power, 
and  the  shell,  if  of  metal  having  a  tenacity  of  60,000  pounds 
per  square  inch  (4218  kgs.  per  sq.  cm.),  would  be,  if  double- 
riveted  in  the  longitudinal  seams,  as  in  Fig.  77,  f  inch  (0.9$ 
cm.)  in  thickness.  The  tubes  would  be  66  or  68  in  number, 
and  the  braces  of  sufficient  number  and  strength  to  sustain 
the  heads  safely.  The  dome  would  be  probably  given  about 
one  half  the  diameter  of  the  boiler,  and  be  made  of  metal  rather 
more  than  one  half  as  thick,  as  it  would  usually  be  single-riv- 
eted. 

The  tubes  should  always  be  placed  in  vertical  and  horizon- 
tal rows;  to  "stagger"  them  would  insure  a  defective  circula- 
tion and  injury  to  those  thus  exposed  to  overheating. 

The  tubes  should  never  be  nearer  than  3  inches  to  the 
shell  of  the  boiler,  and  should  never  be  carried  down  near  the 
bottom  of  the  boiler ;  but  there  should  be  ample  water-space 
at  the  bottom  of  the  shell.  The  fire  from  the  furnace  first 
strikes  the  bottom  of  the  boiler,  and  there  should  be  a  good 
body  of  water  there. 

Pressures  have  risen  in  stationary-boiler  operation  until  the 
common  cylindrical  tubular  boiler  of  6  feet  (1.8  metres)  di- 
ameter is  made  %  inch  (1.27  cm.)  in  thickness  of  shell,  and  is 
safe,  with  usual  construction,  at  a  pressure  of  nearly  ten  at- 
mospheres. 

172.  Marine  Flue-boilers  are  rarely  used  at  sea,  but  remain 
in  use  on  the  rivers  of  the  United  States.  In  their  design,  the 
same  principles  which  have  just  been  applied  are  also  applica- 
ble in  the  determination  of  the  dimensions  of  shell  and  flues. 
The  firebox  forms  an  essential  feature  of  this  class,  however ; 
and  its  construction  involves  calculations  of  strength  of  stayed 
surfaces.  In  the  locomotive,  the  stay-bolts  are  placed  4  or 
5  inches  (10  to  12.7  cm.)  apart,  but  in  marine  boilers  they  are 
more  widely  distributed,  as  working  pressures  are  lower.  In 
any  case,  the  area  of  the  flat  surface  should  be  estimated,  and 
also  the  pressure  upon  it,  and  a  sufficient  number  of  braces 
used  to  provide  for  that  pressure.  If  the  braces  are  of  iron  of 
known  strength,  say  60,000  pounds  per  square  inch  (3515  kgs. 


THE   STEAM-BOILER. 

per  sq.  cm.),  a  factor  of  safety  of  10  would  give  6,000  pound? 
(or  422  kgs.)  on  each  brace  of  unit  section,  and  the  number  of 
braces  should  be  sufficient  to  safely  carry  the  load  on  the  total 
surface.  The  heavier  the  plate,  the  greater  its  resistance  to  the 
distorting  action  of  the  steam-pressure,  and  the  heavier  the 
stay-bolts  and  the  wider  their  spacing.  In  the  older  forms  of 
marine  flue-boiler,  in  which  steam-pressures  ranged  from  25  to 
40  pounds  per  square  inch  (if  to  2§  atmos.),  the  stay-bolts  were 
usually  spaced  from  10  to  8  inches(25  to  20  cm.) apart,  and  were 
given  a  diameter  of  from  one  eighth  to  one  tenth  those  figures. 
This  form  of  boiler  has  so  generally  been  superseded  by  the 
tubular  boiler  that  it  has  now  comparatively  little  importance,, 
except  on  the  large  rivers.  The  following  are  the  proportions 
adopted  on  board  a  number  of  Ohio  and  Mississippi  river 
steamers,  all  of  which  use  the  lap-welded  and  drawn  tube  in 
place  of  the  older  form  of  riveted  flue :  A  steamer  on  the 
Ohio  has  two  boilers,  47  inches  diameter  and  24  feet  long, 
ten  lap-welded  flues  in  each,  of  8  inches  diameter ;  two- 
boilers  41  inches  diameter,  24  feet  long,  with  six  lap-welded 
flues  in  each,  of  10  inches  diameter;  steamer  Golden  Rule, 
three  boilers,  44  inches  diameter,  26  feet  long,  with  three  8- 
and  three  lO-inch  lap-welded  flues  in  each.  Such  flues  are  more 
cylindrical  in  form  than  the  riveted  flue,  thereby  lessening  the 
chances  of  collapsing.  There  are  no  rivet-heads  or  laps  to  in- 
terfere with  the  draught,  and  consequently  the  flues  are  not  li- 
able to  choke  up  with  soot,  are  much  less  apt  to  scale,  and  hav- 
ing smooth  surface,  are  much  more  easily  cleaned. 

The  water-level  should  be  at  least  6  inches  (2.4  cm.)  above 
the  highest  flue,  and  is  usually  fixed  by  law  or  regulation  at  a 
minimum  of  4  inches  (1.6  cm.).  The  highest  line  of  heating- 
surface  is  usually  required  to  be  below  that  level.  Where  ex- 
posed to  flame  these  boilers  are  not  allowed  to  have  a  thick- 
ness exceeding  0.51  inch  (1.2  cm.),  and  a  water-space  of  at  least 
3  inches  (7.6  cm.)  is  left  between  the  flues  and  between  flue 
and  shell. 

173.  The  Marine  Tubular  Boiler  has  now  almost  univer- 
sally been  brought  to  a  very  definite  standard  form  and  propor- 
tions. It  has  been  already  described  as  consisting  of  a  cylin- 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    363 

drical  shell  with  plane  heads,  traversed  by  large  flues  and 
comparatively  small  tubes,  the  furnaces  being  in  the  flues. 
Those  designed  for  sea-going  steamers  are  often  of  very  large 
diameter,  the  steam-pressures  often  exceeding  ten  atmospheres 
(150  pounds  per  square  inch),  they  are  also  made  of  very  heavy 
boiler-plate.  These  boilers  naturally  are  oftener  double- 
riveted  than  those  of  smaller  diameter,  and  every  expedient 
known  to  the  engineer  is  adopted  to  insure  safety.  Diameters 
of  1 5  and  even  of  nearly  20  feet  (4.6  and  nearly  6  m.)  are  com- 
mon, and  plates  as  thick  as  ij  inches  (3.2  cm.)  have  been  used. 
These  heavy  plates  are  usually  butted  at  the  seams,  and  the 
joint  is  covered  with  a  "  butt-strap"  or  "  covering-strip,"  double- 
riveted  on  each  side,  thus  presenting  to  the  eye  four  parallel 
rows  of  large  rivets.  The  calculation  of  the  shell  is  made  in 
the  same  manner  as  in  the  cases  of  the  forms  of  boiler  already 
considered.  The  size  is  determined  partly  by  the  conditions 
and  the  method  described  in  §  171,  and  partly  by  the  necessity 
of  getting  the  whole  set  of  boilers  into  a  space  limited  both  as 
to  volume  and  form  by  the  construction  of  the  vessel  and  by 
the  necessity  of  economizing  as  much  as  possible  that  space 
which  might  be  otherwise  used  for  lading  and  passengers.  The 
stays  are  usually  long  rods,  extending  from  end  to  end  in  the 
steam-space,  and  screwed  stay-bolts,  reinforced  with  nuts,  in 
the  water-spaces.  The  dimensions  of  a  steel  and  of  an  iron 
boiler  of  this  class,  as  actually  constructed,  are,  as  given  by  the 
builders,  the  following: 


STEEL    BOILER    FOR   6  ATMOSPHERES    (90  LBS.  PRESSURE). 

Diameter,       16  ft.;  length,       n  ft.;  shell,   •£•  in.  thick. 

4.gm.;  "  3.35m.;  "  2.2  cm.  " 
3  Furnaces,  48  in.  diameter;  ^|  in.  " 

1.2  m.  "  1.3  cm.  " 

250  Tubes,  3J  in.  "  6£  ft.  long 

7.7  cm.       "  1.98  m.      " 

Area  heating-surface 1800  sq.  ft.  (167  sq.  m.). 

Weight  of  boiler 70,000  pounds    (3^,750  kgs.)  nearly. 

"         water 50,000       "         (22,680    "    )      " 

T^tal  weight 120,000       "         (54,43O    "    )      " 


3°4  THE   STEAM-BOILER, 


IRON   BOILER  (SAME  PRESSURE). 

Diameter,       14. 75  ft.;   length,     n    ft.;  shell,  i-J-  in.  thick. 

4.5™.;       "       3. 35m.;  "  2.86cm.      " 

3  Furnaces,       39  in.  diameter;  \\  in.       " 

0.99  m.         "  i»3  cm.     " 

258  tubes,            3£  in.         "  7  ft.  long. 

8.9  cm.       "  2.1  m.  long. 

Area  heating-surface 2000  sq.  ft.  (186  sq.  m.). 

Weight  of  boiler 75,000  pounds  (34,088  kgs.)  nearly. 

"  water... 45,000       "        (20,412  kgs.)       " 

Total  weight 120,000       "        (54,430  kgs.)       " 


The  drawings  herewith  given,  Fig.  78,  illustrate  the  details 
of  this  construction.  Marine  steam-boilers  require  peculiar  care 
in  their  design  and  construction.  They  must  be  as  light  and  as 
small  as  is  possible  consistent  with  the  efficiency  demanded, 
and,  being  exceptionally  liable  to  rapid  corrosion  and  general 
deterioration,  much  depends  on  their  being  so  made  as  to  per- 
mit every  precaution  to  be  taken  to  prevent  such  injury  and 
to  insure  their  preservation.  In  the  construction  of  cylindrical 
shells  the  longitudinal  seams  are  usually  all  double-riveted, 
and  often  even  butt-jointed,  with  double  covering  strips :  this 
is  almost  always  done  in  cases  in  which  very  high  pressures 
compel  the  use  of  heavy  plates. 

In  ordinary  practice,  the  heating-surface  ranges  from  30  to 
40  times  the  grate-area ;  the  evaporation  ranges  from  6  or  8  to 
10  or  ii  pounds  per  pound  of  good  coal  consumed  ;  the  crown- 
sheets  are  carried  as  high  above  the  grate  as  the  form  of  boiler 
allows  ;  the  grate  bars  are  inclined  about  one  in  twelve,  from  front 
to  rear,  and  are  given  a  length  as  little  more  than  6  feet  as  is 
practicable.  In  the  cylindrical  marine  boiler,  in  which  the 
grates  must  be  set  in  furnaces  which  form  the  lower  and  larger 
set  of  flues,  it  is  not  possible  to  secure  either  as  good  a  propor- 
tion of  grate,  or  as  great  height  above  it  as  is  desirable  ;  and 
the  inefficiency  sometimes  noticed  in  boilers  of  this  class  is 
commonly  due  to  these  faults  of  the  furnaces. 

174.  Sectional  and  Water-tube  Boilers  differ  as  radically 
in  their  design  and  construction,  as  in  type,  from  the  shell- 


DESIGNING  STEAM-BOILERS—PROBLEMS  JiV  DESIGN.    3.65 


Boiler  with  Corrugated  Flue. 


Three-furnace  Boiler. 
FIG.  78.— MARINE  STEAM-BOILERS 


366  THE   STEAM-BOILER. 

boilers  which  have  been  here  considered.  As  a  rule,  their  de- 
sign involves  but  little  calculation  of  strength,  as  their  tubes 
and  connections  are  always  vastly  stronger  than  is  absolutely 
necessary  as  a  mere  matter  of  supporting  the  steam-pressure. 
The  "  headers  "  or  other  connections  of  parts  are  commonly 
without  rivets,  and  are  fitted,  piece  to  piece,  with  machine- 
made  "  faced  "  joints,  and  held  in  place  by  bolts.  Some  special 
precautions  are  demanded,  in  designing  this  type  of  boiler,  to 
secure  safety  against  injury,  and  to  avoid  serious  difficulties 
arising  in  management  from  the  comparatively  small  body  of 
water  and  of  steam  carried  by  them,  and  the  consequent  ab- 
sence of  the  self-regulating  power  observed  in  shell-boilers. 

Mr.  Robert  Wilson  states  that  the  following  appear  to  be 
the  points  'that  require  special  attention  in  designing  these 
water-tube  boilers,  to  insure  their  satisfactory  working  and 
durability  : 

(1)  To  keep  the  joints  out  of  the  fire. 

(2)  To  protect  the  furnace-tubes  from  the  sudden  impinge- 
ment of  cold  air  upon  them  on  opening  the  fire-door. 

(3)  To  provide  against  the  delivery  of  the  cold  feed-water 
directly  into  the  furnace-tubes. 

(4)  To  provide   for  a   good   circulation   to   take  away  the 
stearn  from  the  heating-surfaces. 

(5)  To  provide  passages  of  ample  size  for  upward  currents 
so  that  they  may  not  interfere  with  downward  currents. 

(6)  To  provide  passages  of  ample  size,  for  steam  and  water, 
between  the  various  sections  of  the  boiler,  to  equalize  the  pres- 
sure and  water-level  in  all. 

(7)  To  provide  ample  surface  of  water-level  to  permit  the 
steam  to  leave  the  water  quietly. 

(8)  To  provide  a  sufficiently  large  reservoir  for  steam    to 
prevent   the  water  being  thrown  out  by  suddenly  opening  a 
steam  or  safety  valve. 

(9)  To  provide  against  the  flame  taking  a  short  cut  to  the 
chimney,  and  impinging  against  tubes  containing  steam  only. 

The  several  forms  of  this  type  of  boiler  now  becoming  fa- 
miliar have  illustrated  great  ingenuity  in  securing  efficient  and 
novel  arrangement  of  parts,  rather  than  special  knowledge  of 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    367 

the  character  and  strength  of  materials.  Some  of  these  forms 
have  been  already  described,  and  need  not  be  here  further  il- 
lustrated. This  class  of  boiler  is  generally  in  use  on  land,  but 
attempts  have  been  made  to  introduce  them  for  marine  pur- 
poses. 

The  Author  has  under  his  hand  sets  of  drawings  of  marine 
tubular  boilers  for  a  naval  vessel,  and  of  a  "  sectional "  water- 
tube  boiler  intended  for  similar  power  and  the  same  duty,  which 
afford  a  means  of  comparing  standard  designs  of  the  two  types. 
It  does  not  follow,  however,  that  this  comparison  would  in  all 
cases  yield  similar  deductions. 

The  tubular  boiler  has  a  shell  9  feet  (2.74  m.)  in  diameter, 
while  the  other  is  only  5  feet  (1.52  m.).  The  tubular  has  \\  inches 
(3.2  cm.)  thickness  of  metal  between  fire  and  water  where  the  rear 
tube-sheet  sets  into  the  shell ;  the  greatest  thickness  in  the  sec- 
tional boiler,  between  fire  and  water,  is  only  |-  of  an  inch  (9.5 
mm.).  The  shell-boiler  has  a  ratio  of  grate-surface  to  heating-sur- 
face of  i  to  23,  and  the  ratio  of  grate-surface  to  calorimeter  is  7.2 
to  i  ;  the  sectional  has  a  ratio  of  grate  to  heating  surface  of  I  to 
41.3,  and  a  ratio  of  grate-surface  to  calorimeter  of  4.82  to  i, 
which  means  the  ability  to  burn  more  coal  per  unit  of  grate- 
surface. 

The  steam-space  is  practically  identical  in  both,  but  the 
water  in  the  tubulars  weighs  12.6  pounds  against  15.5  pounds 
in  the  sectional. 

The  total  iron-work  of  the  tubular  boilers  is  35^  pounds  per 
sq.  ft.  of  heating-surface,  whereas  in  the  sectional  it  is  25.8. 
The  total  weight  per  unit  of  heating-surface  is  as  48  in  the 
former  to  41  in  the  latter.  The  tabular  comparison  on  page 
368  was  presented  at  the  same  time. 

On  the  other  hand,  it  is  objected,  by  those  who  oppose  the 
introduction  of  these  boilers  on  shipboard,  that  the  following 
considerations  are  too  important  to  permit  their  safe  employ- 
ment.* 

(i)  That  they  usually  occupy  as  much  space  as  shell- 
boilers. 


*  Shock's  Steam-boilers,  pp.  280-1. 


368 


THE    STEAM-BOILER. 


SHELL  TUBULARS. 

SECTIONAL. 

Shell  
Heads 

9  ft.  diameter  X  9  ft 
%  in.  thick. 
%  in.  thick. 
i}4  'n-  thick. 
1322.7  sq.  ft. 
57-3  sq.  It. 

i  sq.  ft.  to  23  sq.  ft. 
169  cubic  ft. 
t  .012  cut>ic  ft.  per  i  1 
"1      sq.  ft.                      )" 
16,660  pounds 

12    6 

47,040 

35-5           " 
63.700 

48.18 
8.27  sq.  ft. 

7  .  2  to  i  sq.  ft. 
6  in. 

Proposed  battery,  14  boilers,  18.517  ~^*~  -j 
sq.  ft.  heating-surface,  802  sq.ft.  grate-  «  £*  5- 
surface.  U1  o  : 
Fire-rooms,  9  ft.  6.  in.  wide. 
Coal  passed  through  whole  length  ?  ^  .= 
of  fire-room.  —  ,—  : 

5  in.  diameter  X  20  ft. 
thick. 
L£  in.  thick. 
None 
3100  sq.  ft. 
75  sq.  ft. 

i  sq.  ft.  to  41.3  sq.  ft. 
392.6  cubic  ft. 
j  .012   cubic   ft.    to    i  ) 
I      sq.  It.                         f 
48,262  pounds 

15-5 
80,221 

25  8 
128,423     " 

41.44        " 
18  sq.  ft. 

4.82  to  i  sq.  ft. 
24  in. 

Proposed  battery,  8  boilers,  24,800  ~^\  5* 
sq.  ft.  heating-surface,  600  sq.ft.  grate-  £  o  ^ 
surface.  °_o  - 
Fire-rooms,  12  ft.  wide.  cr^  ^ 
Coal  passed  through  3  ft.  passage-  !*<3  _. 
1  way. 

Seams  in  fire  
Heating-surface    ... 
Grate  surface  
Ratio  of  grate-surf  e 
to  heating-surface. 

Ratio  of  steam-space 
to  heating-surface. 
Water,  weight  of  — 
Weight  per    sq.  foot 
heating  surface.  . 
Iron-work,  weight  of 
Iron-work  per  sq.  ft. 
heating-surface  
Total  weight  
Total  weight  per  sq. 
ft.  heat-surface  
Calorimeter 

Ratio    of   grate-sur- 
face to  calorimeter. 
Height  of  water-line 
above  crown-sheet. 

(2)  That  they  are  subject  to  rapid  and  serious  fluctuations 
of  water-level  and  steam-pressure. 

(3)  That  the  circulation  is  less  free  and  steady. 

(4)  That,  for  the  above  reason  and  because  of  their  liability 
to  accumulation  of  incrustation,  overheating  is  sometimes  pe- 
culiarly apt  to  take  place. 

Notwithstanding  these  objections,  which  are  undoubtedly 
to  a  certain  extent  valid,  these  boilers  are  thought  likely,  by 
many  engineers,  to  find  their  way  into  use  at  sea. 

Every  good  "  sectional  "  boiler  consists  of  a  system  of  water- 
tubes,  or  their  equivalent,  so  arranged  as  to  permit  a  rapid, 
steady,  and  certain  circulation  ;  a  system  of  "  headers  "  or  con- 
nections by  which  the  steam  and  water  find  their  way  into  the 
steam-space,  where  separation  and  settling  may  occur ;  and  of 
this  steam-space,  usually  in  the  shape  of  a  large  drum  or  set  of 
drums  of  small  section  from  which  the  steam  is  discharged,  dry, 
into  the  steam-pipe,  and  by  it  conveyed  to  the  point  at  which 
it  is  to  be  utilized.  In  some  cases,  the  steam-drum  is  also 
partly  a  water-reservoir,  and  thus  assists  in  producing  a  regu- 
larity of  operation  very  difficult  to  secure  unless  obtained  by 
the  presence  of  a  considerable  body  of  water,  somewhere  in  the 
structure.  In  this  last  case,  the  greatest  care  must  be  taken  to 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    369 

secure  this  drum  against  the  direct  action  of  flame,  the  nest  of 
tubes  being  ordinarily  so  disposed  as  to  intercept  the  gases 
leaving  the  furnace. 

175.  Upright  and  Portable  Boilers  are  chosen  when  the 
location  or  use  is  such  as  demands  concentration  of  space  or 
facility  of  transportation.  The  upright  boiler,  occupying  little 
floor-space,  having,  for  the  small  powers  for  which  it  is  most 
commonly  used,  no  great  height,  and  being  self-contained  and 
thus  requiring  no  setting,  is  a  form  that  meets  these  special 
conditions  most  perfectly.  Its  design  is  precisely  that,  in 
method,  of  the  cylindrical  tubular  boiler,  except  that  it  must 
have  a  firebox.  The  latter  is  made  in  the  form  of  a  short  cy- 
lindrical, upright,  flue,  occupying  so  much  of  the  lower  part  of 
the  boiler  as  will  give  the  needed  height  of  furnace  and  ash- 
pit. The  water-space  between  this  flue  and  the  shell  is  usually 
about  one  tenth  the  diameter  of  the  latter. 

In  the  design  of  this  flue  or  furnace,  care  should  be  taken 
to  introduce  stay-bolts  to  prevent  collapse  from  overpressure 
or  weakness  produced  by  corrosion,  a  method  of  yielding  which 
causes  the  greater  proportion  of  explosions  of  boilers  of  this 
kind.  The  thickness  of  furnace  sides  is  commonly  the  same  as 
that  of  the  shell ;  the  bottom  ring  and  the  tube-sheet,  at  its  up- 
per end,  giving  additional  security  and  making  the  furnace  very 
much  safer  against  accident  so  long  as  it  is  in  good  order. 
The  calculations  of  this  detail  are  the  same  as  for  any  other  cy- 
lindrical flue  subjected  to  external  pressure. 

The  steam -space  in  the  upright  boiler,  as  often  built, 
consists  only  of  the  volume  of  the  upper  part  of  the  boiler 
above  the  water-level,  and  as  the  tubes  occupy  a  considerable 
proportion  of  the  total  volume  of  the  shell,  the  steam-space  is 
correspondingly  restricted.  This  extension  of  the  tubes  above 
the  water-level  to  the  upper  tube-sheet  also  renders  their  upper 
ends  liable,  at  times,  to  injury  by  overheating.  A  better  plan 
is  that  shown  in  §  15,  in  which  the  upper  tube-sheet  is  sunk  be- 
low the  water-level,  and  all  the  steam-space  needed  is  obtained 
by  carrying  the  shell  upward  to  any  desired  additional  height, 
and  connecting  the  two  by  a  frustum  of  a  cone  having  its  upper 
end  no  larger  than  is  needed  for  the  chimney-flue ;  the  tubes. 
24 


370 


THE   STEAM-BOILER. 


are  thus  protected,  and  the  steam-space  made  ample.  The 
same  remarks  apply  to  the  computations  of  this  cone  as  to 
those  of  the  furnace  ;  it  is,  however,  of  stronger  form  and  less 
likely  to  require  staying. 

Tlic  Portable  Boiler  is  sometimes  upright,  as  when  used  by 
itself  independently  of  the  engine,  or  when  it  has  to  carry  the 
frame  of  an  upright  engine  ;  or  it  is  horizontal,  if  of  large  size, 
or  if  forming  the  bed-piece  of  a  horizontal  engine,  as  is  a  more 
common  arrangement.  In  either  case,  no  very  important  dif- 
ference arises  in  either  the  design  or  method  of  construction, 
except  that  somewhat  greater  care  is  taken  to  make  it  safe 
against  injury  either  by  transportation  or  by  the  stresses  com- 
ing of  the  action  of  the  attached  machinery.  It  is  always  bet- 
ter that  the  boiler  should  carry  an  engine  with  its  frame  than 
that  it  should  itself  act  the  part  of  that  member.  In  all  cases, 
the  connection  of  engine  and  boiler  and  of  boiler  with  its  car- 
riage, where  locomotive,  should  be  so  arranged  that  the  changes 
of  form  and  dimension  due  to  variations  of  temperature  and 
the  stresses  caused  by  difference  of  temperatures  of  adjacent 
parts  as  well  as  changes  of  pressures  may  have  no  ill-effect. 

A  good  steam-drum  or  dome  is  of  even  greater  advantage 
on  the  portable  than  on  the  stationary  boiler.  Their  attached 
engines  are  usually  wasteful,  take  steam  in  very  variable  quan- 
tity, and  are  peculiarly  liable  to  cause  "  foaming." 

The  following  are  the  proportions  adopted  for  portable 
engine-boilers  by  a  well-known  firm  of  British  builders :  * 

PORTABLE  ENGINE-BOILERS. 


HEAT-SURFACE  —  SQUARE  FEET. 

GRATE-SURFACE. 

GRATE- 
SURFACE. 

TUBES. 

Horse- 

Horse- 

power. 

Fire- 
box. 

Tubes. 

Total. 

Per 
Horse- 
power. 

Total. 

Per 

Horse- 
power. 

Heat- 
surface. 

Draught- 
way  — 
Sq.  ft. 

power. 

5 

19.6 

81.8 

101.4 

2O.  2 

3-6 

0.72 

28.2 

0.66 

5 

10 

32-4 

161  .9 

194-3 

19.4 

6.2 

0.62 

31-1 

i.  08 

10 

15 

43.0 

228.7 

271.7 

16.9 

8.6 

0.53 

31-6 

1.39 

15 

20 

53-° 

279.2 

332-2 

16.6 

10.5 

0.52 

31-7 

i  .60 

20 

25 

59-3 

34°  -5 

405.8 

16.0 

12.8 

0.51 

31.8 

1.87 

25 

30 

68.1 

408.8 

476.9 

i5-9 

14.9 

0.49 

3i-9 

2-35 

3° 

*  Wansbrough,  p.  8r. 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    $?l 

A  source  of  danger  to  which  the  upright  boiler  is  peculiarly 
liable  is  that  of  " burning"  the  firebox  or  tube-sheet  in  conse- 
quence of  the  collection  of  sediment  in  the  water-legs  about  the 
furnace  or  on  the  lower  tube-sheet.  The  water-leg  is  sometimes 
found  filled  with  solid  matter,  and  the  tube-plate  so  heavily  in- 
crusted  that  the  metal  is  readily  overheated  and  burned.  All 
boilers  of  this  kind  should  be  provided  with  hand-holes  at  the 
level  of  the  crowmsheet  of  the  furnace,  and  so  placed  as  to 
permit  thorough  inspection  and  complete  removal  of  the  sedi- 
ment at  frequent  intervals. 

Comparing  the  vertical  with  the  horizontal  tubular  boiler, 
it  will  be  observed  that  a  large  item  of  expense  is  avoided  in 
the  cost  of  setting  ;  and  that  an  incidental  advantage  is  secured 
for  the  former  in  the  fact  of  its  accessibility  at  all  times, 
whether  working  or  cold,  for  examination  of  the  exterior.  The 
upright  boiler  is  also  less  liable,  while  in  operation,  to  injury 
from  a  small  depression  of  the  water-level ;  the  fire  never  comes 
in  contact  with  its  shell,  and  this  permits  the  safe  use  of  plates 
as  heavy  as  may  be  desired  ;  no  strains  from  unequal  expansion 
are  to  be  apprehended,  and  experience  shows  this  to  be  an  ele- 
ment contributing  to  the  exceptional  durability  of  this  class  of 
boiler.  Its  only  setting  is  a  foundation  with  an  ashpit,  and  its 
connection  to  the  chimney-flue.  In  the  vertical  tubular  boiler, 
loss  of  water,  and  the  falling  of  the  water-level  even  a  consid- 
erable proportion  of  the  whole  depth  of  boiler,  does  not  neces- 
sarily involve  danger ;  and  the  upper  part  of  the  tubes  may  be 
utilized  as  superheating  surface,  and  the  extent  of  the  super- 
heating adjusted  very  conveniently  by  varying  the  water-level. 

Where  the  feed-water  is  not  very  pure,  however,  the  great 
and  often  fatal  objection  to  this  form  of  boiler  arises  in  the 
danger  of  sediment  or  scale  being  deposited  on  the  lower  tube- 
head,  the  furnace-crown,  and  introducing  danger  of  overheating 
and  of  explosion.  A  considerable  proportion  of  the  explosions 
of  this  kind  of  boiler,  which  have  been  investigated,  are  known 
to  have  been  due  to  this  cause. 

176.  "  Locomotive  "  Boilers  whether  stationary  or  actually 
forming  a  part  of  the  locomotive,  are  of  the  same  general  design 
and  construction.  They  consist  of  a  horizontal,  cylindrical, 


372  THE   STEAM-BOILER. 

tubular  boiler,  crowded,  as  far  as  is  safe  and  practically  eco- 
nomical, with  tubes,  and  with  a  firebox  added  as  an  integral 
part  of  the  structure.  In  such  boilers,  designed  to  be  station- 
ary, the  tubes  are  often  larger  than  those  adopted  in  the 
boiler  of  the  locomotive,  as  the  draught  is  commonly  vastly 
less  intense,  and  the  power  demanded  also  comparatively  small. 
The  boiler  of  the  locomotive  represents  the  highest  art  of  the 
engineer  in  the  combination  of  the  essential  desiderata  for  its 
purpose :  great  power  in  small  weight  and  volume,  combined 
with  maximum  economy  of  fuel  consistent  with  such  concen- 
tration of  power. 

The  locomotive  must  always  use  steam  of  maximum 
pressure,  must  use  enormous  quantities  because  of  its  neces- 
sarily great  power,  and  must  be  at  once  safe  and  fairly  econom- 
ical. In  consequence  of  its  exposure  to  the  action  of  its  own 
great  inertia  in  its  constant  motion  over,  often,  an  irregular 
roadbed,  and  because  it  must  sustain  the  stresses  due  to  the 
action  of  its  own  machinery  and  to  frequent  collisions,  of 
greater  or  less  violence,  while  making  up  and  transporting 
trains,  the  whole  structure  must  be  designed  with  especial  re- 
gard to  such  extraordinary  and  unreckoned  strains  as  may  be 
thus  caused.  Since  the  power  demanded  is  a  maximum,  the 
tubes  must  be  as  numerous,  and  therefore  as  small  and  as 
closely  packed,  as  is  possible  without  affecting  sensibly  the 
circulation  of  water  and  thus  losing  steaming  capacity  ; 
and  since  economy  of  fuel  is  hardly  less  important  than  steam- 
ing capacity,  the  tubes  must  have  sufficient  length  to  give  a 
ratio  of  area  of  heating  surface  to  weight  of  fuel  burned  such  as 
will  insure  that  efficiency  found  to  be  practically  desirable. 
With  all  this,  the  designer  must  keep  in  mind  the  special  ne- 
cessity of  compactness  of  structure,  and  of  a  limit  in  weight 
fixed,  in  many  cases,  at  least,  by  the  magnitude  of  the  friction 
on  the  rail  and  the  tractive  power  demanded  by  the  special 
kind  of  work  for  which  the  engine  is  intended.  To  reconcile 
so  many  and  oftentimes  conflicting  conditions,  and  to  secure 
a  maximum  total  efficiency,  is  evidently  a  problem  of  immense 
importance  and  of  corresponding  difficulty,  and  one  which  can 
only  be  fully  solved  by  the  gradual  evolution  of  the  precise 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN.    373 

form  and  proportions  best  fitted  for  each  of  a  number  of  spe- 
cialized types  and  duties,  such  as  is  illustrated  by  the  different 
passenger  and  "  freight  "  or  "  goods  "  engines  now  becoming 
standard. 

The  methods  of  computation  of  size  and  strength  of  parts 
are  in  no  way  peculiar,  and  no  special  consideration  of  them  is 
here  demanded.  Custom  guided  by  experience  has  led  to  the 
production  of  such  proportions  as  are  illustrated  in  standard 
practice. 

Common  faults  of  design  in  this,  as  in  other  forms  of  hori- 
zontal tubular  boilers,  are  the  excessive  crowding  of  tubes  and 
serious  contraction  of  the  water-spaces  about  the  furnace.  It 
would  probably  be  found  advantageous  not  only  to  preserve 
good  water-channels  between  adjacent  tubes,  but  to  leave  out 
a  vertical  row  of  tubes  along  the  diameter  of  the  boiler,  and  to 
allow  an  equal  space  between  the  nest  of  tubes  and  the  shell 
all  around.  This  has  often  been  done  by  good  constructors, 
with  evident  advantage,  when  boilers  are  doing  much  work. 
It  is  a  safe  arrangement  to  adopt  for  all  cases.  Water-legs 
should  be  made  to  widen  from  the  bottom  upward. 

The  crown-sheet  is  supported  by  girders,  "  crown-bars,"  rest- 
ing at  each  end  on  the  upper  edge  of  the  side  sheets  of  the 
furnace  and  carrying  the  load  by  stays  set  at  frequent  intervals 
in  their  length.  They  should  be  very  carefully  designed. 
Stays  to  the  shell  are  unsafe. 

The  material  used  .in  this  class  of  boiler  is  becoming  univer- 
sally soft  steel,  containing  so  little  carbon  that  it  will  not  tem- 
per. Harder  steels  crack  in  the  firebox-sheets,  especially  where 
deep  and  hard-worked.  The  thickness  of  the  shell  is  often  re- 
duced 15  or  20  percent,  as  compared  with  iron.  Good  steel 
neither  cracks  nor  blisters.  Asa  rule,  with  steam  at  120 pounds, 
the  general  practice  is,  in  the  United  States,  to  use  -f-inch  iron 
or  steel  for  outside  sheets,  T5^  inch  iron  or  steel  for  fireboxes, 
and  from  -§•  to  j-  inch  for  tube-sheets.  Water-spaces  around 
firebox  from  2\  to  3^  inches  inside,  and  from  2f  to  4  inches  in 
front.  At  straight  seams  \\  inch  rivets  are  used,  spaced  if 
inches  between  centres.  Longitudinal  seams  double-riveted, 
centres  of  the  two  lines  of  rivets  ij  inches  apart,  centre  to  cen- 


374  THE   STEAM-BOILER. 

tre  of  rivets  on  same  line  2f  inches.  Stay-bolts  \  inch  di- 
ameter, 4  inches  centre  to  centre.  It  is  thought  that  thin 
plates  give  the  best  result  in  fireboxes,  sides  and  back  of 
£-inch  steel,  crown-sheet  T5¥-inch  steel,  and  tube-sheet  f  inch. 
Tube-sheets  of  T^-inch  iron,  the  other  plates  being  steel,  have 
also  given  good  results.  It  is  believed  that  ^-inch  steel  plates 
are  strong  enough  for  side  sheets  and  less  liable  to  crack  than 
thicker  plates.  Crown-sheets  are  more  easily  straightened 
when  sagged  down  from  mud  collecting,  and  will  not  crack 
so  quickly  from  overheated  crown-bar  bolts. 

The  life  of  a  good  boiler  is  usually  from  ten  to  twelve  years. 
Tubes  are  removed  to  permit  inspection  every  three  or  four 
years.  Steel  and  iron  are  now  used  for  wood-burning  fireboxes, 
with  a  result  usually  declared  to  be  in  favor  of  steel,  in  conse- 
quence of  the  lighter  sheets  and  the  metal  not  blistering. 
With  bituminous  coal  copper,  steel,  and  iron  are  used.  Copper 
will  not  crack,  but  wears  away,  and  is  soon  reduced  to  a  dan- 
gerous thinness.  A  copper  firebox  lasts  from  three  to  five 
years,  The  objection  to  iron  fireboxes  is  that  the  iron  blisters, 
becomes  "  burnt  "  and  very  brittle,  and  cracks.  Three  years  is 
the  average  life  of  an  iron  firebox.  The  only  objection  to 
steel  is  that  it  sometimes  cracks.  The  average  life  of  the  best 
is  9  years  and  6  months ;  of  the  worst,  4  years  and  4  months ; 
of  the  total  reported,  6  years  and  4  months. 

The  following  is  considered  a  good  specification  for  a  steel 
locomotive  boiler: 

Boiler  to  be  made  of  mild  steel  T\-  inch  thick,  riveted  with 
f-inch  rivets  placed  not  over  2J-  inches  from  centre  to  centre  ; 
all  horizontal  seams  and  junction  of  waist  and  firebox  double 
riveted ;  all  longitudinal  seams  provided  with  lap  welt,  with 
rivets  alternating  on  both  sides  of  main  seams,  to  protect  calk- 
ing edges,  and  all  parts  well  and  thoroughly  stayed ;  top  and 
sides  of  outside  firebox  all  in  one  sheet ;  back-head  a  perfect 
circle.  All  plates  planed  on  edges  and  calked  with  round- 
pointed  calking  tools,  insuring  plates  against  injury  by  chipping 
and  calking  with  sharp-edged  tools.  Boiler  tested  with  180  Ibs, 
to  the  square  inch,  steam-pressure.  Waist  52  inches  in  diame- 
ter at  smoke-box  end,  made  wagon-top  with  extended  arch  with 


DESIGNING   STEAM-BOILERS—PROBLEMS  IN  DESIGN     3/5 

one  dome  30  inches  diameter  on  the  wagon-top  ;  tubes  of  char- 
coal-iron, No.  12  B,  wire-gauge,  200  in  number,  2  inches  outside 
diameter  and  1 1  feet  8f  inches  in  length,  with  copper  ferrules 
on  firebox  end;  firebox  made  of  mild  steel,  78  inches  long  and 
34  inches  wide  ;  all  plates  thoroughly  annealed  after  flanging ; 
side  T5F  and  back-sheets  f  inches  thick ;  crown-sheet  f  inches 
thick ;  flue-sheet  ^  inch  thick ;  water-space  5  inches  wide  at  sides, 
3-J  inches  wide  at  back,  and  3^  to  4-|-  inches  wide  at  front ; 
stay-bolts  -J  inch  diameter,  screwed  and  riveted  to  sheets,  and 
not  over  4^  inches  from  centre  to  centre ;  fire-door  opening 
formed  by  flanging  and  riveting  together  the  inner  and  outer 
sheets ;  2  rows  of  hollow  stay-bolts  above  fire  ;  2  rows  of  telltale 
stay-bolts  at  top  on  sides ;  crown  supported  by  crown-bars,  each 
made  of  two  pieces  of  5  X  |  inches  wrought-iron  ;  placed  not 
over  4£  inches  between  centres,  bars  to  extend  across,  with  ends 
resting  on  castings  on  the  side-sheets ;  crown-bar  bolts  -J  in. 
diameter,  with  flat  heads  under  the  crown-sheet,  the  fit  in  the 
crown-sheet  to  be  tapered  and  drawn  to  its  place  by  a  nut 
above  the  crown-bar;  the  crown  to  be  well  and  thoroughly 
stayed  by  braces  to  dome  and  outside  shell  of  boiler ;  clean- 
ing holes  in  corner  of  firebox,  and  blow-off-cock  in  side ;  smoke- 
stack straight ;  grates  cast-iron,  rocking  with  dump ;  ash-pan 
wrought-iron,  dampers  front  and  back ;  balanced  poppet 
throttle-valve  of  cast-iron  in  vertical  arm  of  dry-pipe. 

The  firebox  first  introduced  by  Mr.  Wooten  on  the  Phila- 
delphia and  Reading  Railway  is  carried  higher  than  ordinary,  so 
as  to  obtain  room  for  broadening  the  grate  and  thus  enlarging 
it,  so  as  to  be  capable  of  successfully  burning  the  hitherto  use- 
less anthracite  culm.  The  dimensions  of  their  common  loco- 
motive firebox  are  60  and  66  by  32  inches ;  the  first  of  new 
design  is  8  feet  6  inches  long  by  7  feet  6£  inches  wide  ;  the 
heating-surface  of  the  firebox  is  106  square  feet,  and  of  the 
combustion-chamber  26  feet,  making  a  total  of  982  square  feet. 
The  grate-rest  is  between  water-bars  to  prevent  burning  out, 
and  the  area  is  64  feet.  The  consumption  of  coal  is  only  16 
pounds  per  hour  per  square  foot  of  grate-surface  against  40  to 
60  pounds  in  the  ordinary  locomotive. 

The  fuel  remains  perfectly  quiet  in  the  firebox,  the  consump- 


THE   STEAM-BOILER. 


tion  is  slow,  the  steam  is  more  freely  made  than  in  the  common 
style  of  locomotive  boiler,  and  no  smoke  or  sparks  are  ejected 
from  the  smoke-stack. 


FIG.  79.— STATIONARY  "  LOCOMOTIVE"  BOILER. 


The  stationary  boiler  of  the  locomotive  type  is  shown  in  the 
accompanying  figure,  as  customarily  mounted  on  skids  for 
transportation,  with  gauge-cocks,  water-gauge,  steam-gauge,  and 
safety-valve  attached,  and  in  working  order. 


CHAPTER  IX. 

DESIGNING    ACCESSORIES — SETTING — CHIMNEYS. 

177.  The  Setting  of  Boilers  which  are  not  self-contained 
involves  the  construction  of  a  system  of  side-walls  and  bridge- 
walls,  customarily  of  brickwork,  and  entails  so  great  an  expense 
as  often  to  make  the  question  of  the  adoption  of  the  firebox  or 


TUBULAR  BOILER. 


the  plain  boiler  one  of  serious  importance.  It  is  usually  found 
to  be  economical  to  adopt  the  firebox  boiler  for  small  powers, 
and  to  employ  the  other  type  where  large  quantities  of  steam 
are  to  be  made. 

The  form  of  the  setting,  the  arrangement  of  bridge-walls,  and 
the  number,  size,  and  disposition  of  flues,  are  all  matters  of 
ready  determination  once  the  style  of  boiler  is  settled  ;  but 
while  the  best  engineers  have  come  to  a  nearly  uniform  and 


378 


THE   STEAM-BOILER. 


standard  design,  a  great  variety  of  forms  and  proportions  are 
actually  in  use  for  every  one  of  the  familiar  boilers.  General 
practice  prescribes  the  use  of  a  cast-iron  front  protected  from 
the  action  of  the  fire  by  a  fire-brick  lining.  Side-walls  are  of 
red  or  common  brick,  lined  with  fire-brick  wherever  exposed  to 
the  direct  action  of  the  flame.  The  bridge-wall  adjacent  to  the 
furnace  is  of  fire-brick,  except  in  parts  so  located  as  to  be  pro- 
tected from  the  impinging  flame  ;  and  the  flues,  even,  are  some- 
times similarly  lined.  The  brickwork  is  held  in  place  and  the 
whole  structure  kept  together  by  tie-rods  and  binding-bars,  of 
which  the  fastening  bolts  are  so  located  as  to  be  exposed  only 
to  moderate  temperatures. 

The  following  figure  illustrates  such  a  setting  for  a  horizon- 
tal tubular  boiler  of  good  proportions  : 


FIG.  81. — SETTING  OF  HORIZONTAL  TUBULAR  BOILER. 

Here  a  set  of  12-inch-side  walls  are  lined  with  an  inner  wall, 
and  an  air-space  between  intercepts  the  heat,  and  is  itself  partly 
or  wholly  of  fire-brick.  Vertical  binders  on  each  side,  tied 
together  by  heavy  transverse  bolts  at  top  and  bottom,  hold  all 
in  place  ;  and  similar  bolts  tie  the  front  to  the  rear  wall.  The 
bridge-wall  is  set  inside,  at  the  rear  of  the  grates,  and  is  raised 
just  high  enough  to  prevent  fuel  falling  or  being  thrown  back 
under  the  boiler. 

The  practice  of  the  Hartford  Boiler  Insurance  Co.  is  illus- 
trated by  the  next  figure,  in  which  are  given  the  dimensions  of 
setting  for  a  "  6o-inch"  tubular  boiler,  as  published  in  the  speci- 


DESIGNING  A  CCESSORIP:S—SE  TTING—CHIMNE  vs.      3  79 

fication.     In  this   sketch  the  fire-brick  used  in  lining  the  walls 
is  sharply  distinguished  from  the  remainder. 

Where  no  circulation  is  permitted  there  is  no  objection  to 
allowing  the  spaces  above  and  below  the  boiler  to  communicate. 
In  some  cases  the  space  above  the  boiler,  when  closed  in,  is 
used  as  a  flue,  with  the  effect  of  drying,  and  sometimes  of 
superheating,  the  steam.  There  is  an  unquestioned  advantage 
in  keeping  the  boiler  as  nearly  of  uniform  temperature  as  pos- 
sible ;  but  many  engineers  consider  this  system  to  involve  some 
risk.  The  suspension  of  the  boiler  is  a  matter  demanding  the 
greatest  care.  It  was  formerly  the  custom  to  pay  little  atten- 
tion to  this  matter  ;  but  the  occasional  explosion  of  a  boiler  in 
consequence  of  irregular  strains  so  induced,  has  led  to  more 


FIG.  82. — SETTING  OF  TUBULAR  BOILER. 

careful  design.  The  most  common  system  is  probably  that  in 
which  the  boiler  has  a  set  of  cast-iron  lugs  riveted  on  its  sides 
and  resting  on  plates  built  into  the  brickwork  of  the  side-walls, 
thus  distributing  the  weight.  In  some  cases  the  boiler  is  sus- 
pended from  transverse  girders  resting,  at  each  end,  on  the  side- 
walls  of  the  setting ;  and  the  heads  of  the  supporting  bolts  have 
sometimes  been  carried  on  springs  to  insure  an  equalization  of 
load  and  its  uniform  and  safe  distribution — which  is  the  essen- 
tial aim  of  all  good  systems  of  support.  Where  twro  points  of 
support  are  chosen  on  each  side,  they  should  be  placed  one 
fourth  the  length  of  the  boiler  from  each  end  ;  where  three 
supports  are  introduced,  the  outer  ones  should  be  one  sixth 
the  length  of  the  boiler  from  the  ends,  and  the  third  should  be 


380  THE   STEAM-BOILER. 

placed  in  the  middle,  thus  giving  a  uniform  load  on  all. 
Horizontal  boilers  are  sometimes  supported  at  the  rear  end  on 
plates  resting  on  rollers  to  reduce  frictional  resistance  to  change 
of  dimensions. 

It  is  probably  as  well  not  to  attempt  to  carry  the  weight  of 
the  boiler  on  the  walls  of  its  setting,  and  this  can  be  avoided 
by  adopting  the  plan  of  inserting  vertical  posts,  made  of  a  pair 
of  channel-bars  secured  back  to  back,  and  thus  forming  strong, 
simple,  and  inexpensive  columns,  on  which  the  load  can  be 
safely  and  permanently  carried.  The  air-space  between  the 
walls  is  an  important  safeguard  against  injury  by  the  change  of 
form  of  the  inner  wall  with  variation  of  temperature.  Where 
desirable,  the  space  between  the  boiler  and  this  continually 
moving  mass  can  be  closed  by  carrying  a  flange  of  angle-iron 
along  it,  and  supporting  this  flange  from  the  iron  posts  in  the 
walls.  Angle  and  channel  irons  are  also  best  for  use  in  making 
the  binders  or  "  buckstaves"  by  which  the  whole  setting  is 
kept  in  shape.  Where  cast-iron  is  used  at  all,  as  in  the  fronts, 
it  should  be  heavy  enough  to  keep  its  shape. 

Where  a  boiler  is  supported  by  lugs  riveted  to  its  sides  and 
bearing  on  the  side-walls  of  the  setting,  the  principal  risk  is 
usually,  probably,  that  of  the  failure  of  the  riveting.  The 
boiler-shell  has  a  large  margin  of  strength,  and  no  injury  need 
ordinarily  be  feared  from  the  stress  coming  of  its  own  weight 
between  the  points  of  support.  When  the  rivets  are  placed  not 
more  than  four  or  five  diameters  apart,  the  boiler  may  be  con- 
sidered as  perfectly  safe,  the  workmanship  being  good.  It  is 
advisable  to  place  covering  strips  on  the  inside  to  take  the 
heads  of  the  rivets  securing  the  lugs  in  place. 

178.  Forms  of  Covering  to  prevent  the  loss  of  heat  from 
the  boiler  and  flues  by  conduction  and  radiation  are  of  consid- 
erable variety.  The  rudest,  though  an  effective  one,  is  a  layer 
of  ashes  over  the  top  of  the  boiler,  filling  in  between  the  side- 
walls  of  the  setting.  This  is  often  objectionable,  as  giving  rise 
to  annoyance  from  dust ;  and  various  mineral  and  fibrous  sub- 
stances are  preferred,  such  as  asbestos,  hair-felt,  and  several 
kinds  of  plaster  and  cement.  Where  hair-felt  is  used,  it  is 
often  covered  with  canvas  to  give  a  neater  appearance,  and  to 


DESIGNING  A  CCESSORIES—SE  TTING-  CPIIMNE  VS.        3 8  I 

protect  the  felt  from  dust  and  injury.  Occasionally,  a  brick 
arch  is  turned  over  the  whole  structure,  and  the  air-space  so 
produced  relied  upon  to  intercept  heat.  This  construction  is 
probably  not  quite  as  efficient  as  the  other  coverings,  but  it 
has  the  advantage  of  permitting  easy  access  to  the  boiler  for 
inspection  and  repair. 

179.  The  Form  of  the  Bridge-wall  is  not  always  the  same 
in  the  same  general  design.  A  bridge-wall  is  needed  at  the  rear 
end  of  the  grate,  and  it  is  now  rather  unusual  to  build  others ; 
but  two,    or   even    more,    are    sometimes    introduced    for   the 
alleged    purpose  of  securing  intermingling  of  the  currents  of 
furnace-gas  and  their  contact  with  the  boiler.     In  some  cases 
the    bridge-wall  is  carried  up  to   the    boiler-shell    nearly,   and 
fitted  rather  closely  to  its  form;  a  more  approved  system,  how- 
ever, gives  its  top  a  perfectly  straight  and  level  line.     Ample 
space  should  always  be  allowed  for  the  passage  of  the  gases,  as 
well  as  above  the  grates,  for  the  completion  of  combustion.  The 
semi-diameter  of  the  boiler  is  none  too  great  for  the  depth  of 
this  latter  space. 

180.  The  Disposition  of  Flues  is  subject  to  the  same  re- 
mark as  was  made  relative  to  the  bridge-wall.     No  standard 
practice  can  be  described  ;  but  it  is  continually  becoming  more 
usual   to   leave    the  whole    space  beneath  the    boiler  without 
subdivision    from  bridge-wall    to  chimney-flue,  taking   off  the 
gases  from  the  tubes  as  directly  to  the  chimney  as  possible,  and 
controlling   the  flow  of  the  gas-current  by  the  damper.       Oc- 
casionally a  special  direct  flue  is  provided  with  its  own  dam- 
per, when  a  drop  flue  is  ordinarily  used,  or  when  the  flame  is 
carried  over  the  shell,  the  former  being   opened  when  the  fires 
are  started  to  secure  rapid  kindling,  and  closed  again  when  the 
fires  are   fairly  burning.     The  shortest  line   of  flue  from   the 
boiler-setting  to  the  chimney  is  best  in  all  cases. 

181.  The  Location  and  Design  of  Chimney  may  often  be 
the  first  step  to  be  taken  preliminarily  to  designing  the  boiler ; 
or,  as  is  oftener  the  case,  the  user  purchases  his  boiler  and  then 
erects  such  a  chimney  as  the  designer  and  vender  may  recom- 
mend, in  such  location  as  he  may  find  practicable.     In  many 
cases  the  chimney  consists  of  a  simple  pipe  of  sheet-iron,  ris- 


THE    STEAM-BOILER. 

ing  directly  from  the  flue,  which,  forming  part  of  the  boiler  set- 
ting, also  serves  as  the  base  of  the  pipe.  In  this  case  the  rules  for 
proportioning  are  to  be  taken  as  those  governing  marine  prac- 
tice, and  the  draught  as  calculable  on  that  basis,  with  a  consid- 
erable margin  to  allow  for  variations  of  temperature,  humidity, 
and  mobility  of  atmosphere.  In  the  majority  of  cases,  how- 
ever, a  chimney-stack  of  brickwork  is  preferred,  both  on  the 
score  of  permanence  and  on  that  of  better  draught  ;  the  iron  flue 
permitting  a  loss  of  heat  and  cooling  of  the  air-column,  which 
does  not  take  place  to  any  observable  extent  in  the  brick 
stack.  No.  10  or  12  iron  is  ordinarily  used. 

The  essentials  of  a  good  design  are  :  adaptation  in  draught 
power  and  capacity,  in  height  and  area  of  flue,  to  the  precise 
conditions  to  be  met,  with  ample  surplus  for  emergencies ;  a 
solid  and  perfectly  safe  foundation  ;  a  well-formed,  straight, 
well-proportioned  shaft ;  stability  against  the  pressure  of  the 
most  violent  winds  ;  security  against  injury  by  its  own  heated 
gases  ;  and  economy  in  construction  and  maintenance.  The 
first  two  of  these  requirements  are  met  by  the  methods  already 
detailed  in  §  160:  a  safe  foundation  is  obtained  by  going  down 
to  the  rock  wherever  possible,  or  to  firm,  compact,  stable  soil, 
and  there  starting  the  bed  courses,  giving  them  ample  area  to 
carry  the  superincumbent  weight  safely.  Where  difficulty  is 
met  with  in  the  endeavor  to  accomplish  this,  a  broad  concrete 
base  is  often  laid  on  the  yielding  substratum  of  soil,  and  on 
this  the  masonry  is  laid  up  after  ample  time  for  hardening  and 
settling  is  allowed.  The  more  slowly  the  construction  is  car- 
ried on,  the  better  the  result.  The  form  and  proportion  of  the 
shaft  is  partly  a  matter  of  taste,  judgment,  and  architectural 
effect,  and  partly  of  calculation  based  on  the  elements  pre- 
scribed by  the  conditions  under  which  the  boiler  is  to  be  oper- 
ated. Stability  is  assured  by  carefully  proportioning  weight 
of  stack  and  breadth  at  the  foundation  to  meet  the  overturn- 
ing force  of  the  highest  winds,  and  allowing,  further,  a  fair  fac- 
tor of  safety.  A  pressure  of  55  pounds  per  square  foot  (268 
kgs.  per  sq.  m.)  on  chimneys  of  square  section,  and  one  half 
this  amount  on  chimneys  of  circular  or  octagonal  section,  is  a 
common  assumption  as  a  measure  of  the  maximum  force  of 


DESIGNING  ACCESSORIES—  SET  7^1  NG—  CHIMNEYS.        383 

the  wind  in  exposed  situations.  In  sheltered  localities,  a  cal- 
culation of  stability  is  rarely  made.  Security  against  the  cut- 
ting or  overheating  which  may  sometimes  occur  where  the  fur- 
nace gases  reach  the  chimney  at  a  very  high  temperature  is 
obtained  in  large  chimneys  by  the  construction  of  an  inner 
chimney  of  fire-brick,  separated  from  the  main  structure  by  a 
narrow  air-space.  In  small  chimneys  a  lining  of  fire-brick  built 
into  the  walls  of  the  chimney  for  some  distance  upward  from 
the  base  is  the  usual  safeguard,  and  even  this  is  often  omitted. 
Economy  is  obtained  by  making  the  design  as  simple,  the 
height  and  the  dimensions  generally  as  small,  as  may  be  con- 
sistent with  a  good  design. 

Circular  and  octagonal  sections  are  best  as  a  rule,  but  the 
square  section  is  usually  the  least  costly  to  build.  Where  an 
outer  and  an  inner  shell  are  put  up  separately  from  the  foun- 
dation, provision  is  often  made  to  cover,  in  some  way,  the 
annular  opening  between  the  two  at  the  top  of  the  inner  stack 
to  prevent  the  settlement  of  dust  between  them :  this  is  not, 
however,  usual  or  essential  ;  but  a  cleaning  door  should  be 
placed  at  the  bottom,  through  which  access  can  be  had  both 
to  this  space  and  to  the  main  flue.  All  the  talent  of  the  archi- 
tect is  often  demanded  in  the  design  of  the  exterior  of  large 
chimneys. 

The  following  are  the  dimensions  of  a  large  chimney  of  good 
design  \* 

Height  above  grade 192  ft.  58.5  m. 

Total  height  (with  foundation). . .  204  ft.  62.18  m. 

Batter. ...    2  in  100,  nearly. 

Diameter  at  grade 17  ft.  5.18  m. 

of  flue  at  top 8ft.  2.43m. 

Thickness,  stack 2  67  to  1.33  ft.         0.8  to  0.4  m. 

inner  shell 1.33  to  0.67  ft.         0.4  to  0.2  m. 

Weight 2, 187  tons.  2,222  tonnes. 

Horse-power 2.700. 

Cost  per  H.-P $5-53. 

"     total $14  ooo. 

182.  Steam  and  Water  Pipes  and  their  connections  should 
be  as  carefully  designed  and  located  as  the  members  of  the 

*  Sci.  Am.  Supp.,  Jan.  29,  1887. 


384  THE   STEAM-BOILER. 

structure  itself.  Steam  should  be  taken  off  at  the  point  at 
which  it  will  pass  out  most  perfectly  dry,  or,  if  provision  is 
made  for  it,  superheated.  If  a  steam-dome  is  attached  to  the 
boiler  it  should  usually  be  placed  at  a  distance  from  that  part 
of  the  steam-space  into  which  steam  is  rising  most  rapidly,  and 
the  steam-pipe  should  be  led  from  the  highest  point  within 
it.  If  a  dry  pipe  is  used  it  is  better  to  so  place  it  that  its  most 
contracted  openings  are  nearest  the  furnace.  Such  area  should 
be  given  this  pipe  that  the  frictional  resistance  to  flow  should 
not  sensibly  reduce  its  pressure,  and  the  same  precaution 
should  be  taken  in  placing  valves.  A  velocity  of  6000  feet 
(1829  m.)  per  minute  should  usually  be  a  maximum  rate  of  flow. 
The  steam-pipe  should  be  as  carefully  protected  by  non- 
conducting covering  as  the  boiler  itself,  and  it  should  be  so  set 
and  drained  that  no  water  can  collect  at  low  points  or  in  an- 
gles, to  be  thrown  forward  by  the  steam  into  the  engine,  there 
to  cause  danger  of  accident.  The  Author  has  frequently  known 
this  to  occur,  and  the  steam-pipe  itself  is  sometimes  burst  open 
by  its  impact,  causing  loss  of  both  life  and  property.  Experi- 
ments conducted  by  the  Author*  have  shown  that  pressures 
produced  by  this  so-called  "  water-hammer  "  may  amount  to 
probably  above  ten  times  that  which  the  pipe  was  expected  to 
sustain  in  regular  work.  Drain-cocks  and  steam-traps  suitably 
placed  may  be  used  to  take  away  water  collecting  in  bends 
where  they  are  unavoidably  introduced.  Care  must  be  taken, 
in  long  straight  lines  of  pipe,  to  avoid  danger  of  injury  by  the 
expansion  and  contraction  taking  place  with  change  of  temper- 
ature as  the  pipe  is  heated  and  cooled  when  steam  is  sent 
through  it  or  when  emptied.  Where  precautions  are  not  taken, 
as  in  the  introduction  of  bends,  angles,  or  slip-joints  or  their 
equivalents,  pipes  are  sometimes  broken,  joints  are  set  leaking, 
or  connections  are  completely  broken,  and  serious  results  fol- 
low. If  extensive  systems  of  pipe  are  properly  guarded  against 
water-hammer  and  excessive  temperature-strains  by  correct  lo- 
cation, thorough  drainage,  and  good  designing,  no  other  dan- 
ger than  that  of  corrosion  is  to  be  apprehended. 


*  Trans.  Am.  Soc.  Mec.  Engs.,  vol.  iv.,  1882-83,  p.  404. 


DESIGNING  A  CCESSORIES—SE  TT1NG—  CI1IMNE  YS.        38  $ 

Similar  principles  control  the  location  and  proportioning  of 
feed-water  pipes.  They  should  be  of  ample  size  and  strength, 
should  be  so  located  as  to  be  free  from  liability  to  injury  by 
expansion  and  contraction,  and  should  be  led  into  the  boiler  in 
such  manner  and  should  so  discharge  the  feed-water  that  in- 
jury should  not  be  done  the  boiler  by  the  impinging  of  cold 
water  on  heating-surfaces,  or  by  the  collection  of  a  mass  of  cold 
water  at  times  in  the  lower  part  of  the  boiler,  thus  introducing 
serious  strains,  along  the  line  separating  the  cold  from  the  hot 
water,  or  elsewhere.  The  entering  feed  should  be  warmed  by 
flowing  out  into  the  general  mass  of  circulating  liquid,  and 
should  not  be  so  directed  as  to  impinge  on  metal.  No  calcu- 
lations of  strength  of  ordinary  steam  and  water  pipe  are  ordi- 
narily made,  as  the  internal  pressure  is  usually  the  least  impor- 
tant stress  affecting  them.  If  strong  enough  to  bear  other 
stresses  and  thick  enough  to  resist  corrosion  for  a  considerable 
time,  they  are  amply  strong. 

All  cocks,  valves,  and  connections  should  be  strong  enough 
and  sufficiently  well  put  together  to  bear  safely  such  accidental 
stresses  as  have  been  referred  to  without  risk. 

183.  Safety-valves  are  absolutely  essential  to  every  steam- 
boiler.  Many  explosions  have  been  known  to  have  been  caused 
by  the  failure  of  a  safety-valve  to  open  at  the  intended  pres- 
sure, and  it  is  considered  good  practice  to  evade  such  a  danger 
by  introducing  two  safety-valves  into  the  design  of  every- 
boiler. 

The  office  of  a  safety-valve,  as  used  on  a  steam-boiler,  is  to 
discharge  steam  so  rapidly,  when  the  pressure  within  the  boiler 
reaches  a  fixed  limit,  that  no  important  increase  of  pressure  cam 
then  occur,  however  rapidly  steam  may  be  made.  It  has  also 
another  office  :  it  should  be  so  constructed  and  arranged  that 
should  any  accident  occur  it  may  be  opened  by  hand  and  the 
steam-pressure  lowered  very  rapidly,  even  when  the  fires  in  the 
boilers  are  burning  brightly  and  generating  steam  with  maxi- 
mum rapidity.  The  size  of  a  safety-valve  is  determined  by  the 
character  of  the  valve  itself,  by  the  pressure  at  which  the  steam 
is  to  be  discharged,  by  the  difference  permissible  between  the 
pressure  at  which  the  valve  is  to  open  automatically,  and  that 
25 


386  THE    STEAM-BOILER. 

at  which  it  is  intended  to  be  capable  of  discharging  steam  as 
fast  as  the  boiler  can  make  it. 

A  valve  of  defective  design  or  badly  constructed  must  nec- 
essarily be  larger,  to  do  the  same  work,  than  one  of  similar 
type  well  designed  and  constructed.  Steam  is  discharged  at 
any  given  rate  through  an  orifice  of  smaller  dimensions  as  the 
pressure  increases ;  the  lower  the  pressure,  on  the  other  hand, 
the  larger  must  be  the  valve.  A  boiler  in  which  steam  is  car- 
ried at  ordinary  pressure  may  require  a  safety-valve  of  large 
area,  while  the  same  quantity  of  steam  would  escape  through  a 
rivet-hole  in  a  boiler  containing  steam  at  pressures  sruch  as 
were  attained  by  Perkins  and  Albans  a  generation  ago. 

Rules  by  which  to  calculate  the  proper  area  of  safety-valves 
for  every  case  arising  in  his  practice  are  used  by  every  engineer 
accustomed  to  designing  steam-boilers.  These  rules  vary  con- 
siderably with  differences  in  the  experience  or  the  judgment 
of  their  authors. 

But  a  safety-valve,  as  has  been  stated,  should  be  capable  of 
discharging  very  much  more  than  the  maximum  quantity  of 
steam  that  the  boiler  can  make  when  doing  its  best.  The 
valve  must  be  raised,  ordinarily,  by  the  action  of  the  steam  it- 
self, and  the  force  exerted  by  the  steam-pressure  upon  its  disk 
rapidly  diminishes  as  it  rises  from  its  seat.  The  seat  is  bev- 
elled, too,  in  such  a  manner  that  the  effective  area  for  dis- 
charge of  steam  is  but  a  fraction  of  that  due  the  rise  of  a  valve 
having  an  unbevelled  seat.  It  is  therefore  advisable  to  give  a 
very  large  area  to  the  valves. 

It  has  been  common  in  the  United  States  to  allow  but 
one  square  inch  of  area  of  valve-opening  for  25  square  feet  of 
heating-surface,  or  a  ratio  of  0.0003,  nearly ;  while  another  rule 
gives  one  square  inch  to  three  feet  of  grate-surface :  an  English' 
rule  allows  an  area  equal  to  a  half  square  inch  to  a  square  foot 
of  grate,  or  0.003  the  grate-surface,  nearly  ;  while  still  another 
•authority  nearly  doubles  this  area  of  valve.  But  the  area 
should  always  be  based  on  the  quantity  of  steam  made.  The 
Author  has  been  led  by  experience  to  adopt  the  rule :  Multiply 
the  maximum  weight  of  steam  which  the  boiler  is  expected  to 
generate  per  hour  by  five  and  divide  by  ten  times  the  gauge- 


DESIGNING  A  CCESSORIES— SETTING— CHI MNE  VS.        38? 

pressure,  increased  by  ten,  in  British  measures ;  or,  divide  that 
weight  by  twice  the  latter  quantity.     Thus, 


where  w  is.  the  maximum  weight  of  steam  made  per  hour  in 
pounds,  /  the  pressure  in  pounds  on  the  square  inch,  and  a  the 
area  of  the  valve-opening  in  square  inches. 

For  important  work  it  is  advisable,  especially  for  large 
boilers,  to  calculate  carefully  the  area  of  opening  needed,  by 
the  principles  controlling  the  discharge  of  steam  from  orifices. 
A  very  large  excess  over  the  area  demanded  to  just  discharge 
steam  at  the  maximum  rate  at  which  it  is  made  should  be 
given,  as  it  is  often  necessary  to  rapidly  reduce  pressure  just 
when  the  fires  are  brightest  and  vaporization  most  active. 
The  design  of  the  valve  is  rarely  a  problem  solved  by  the  de- 
signer of  the  boiler.  Valves  in  great  variety  are  made  and 
sold  by  manufacturers,  and  it  is  customary  to  purchase  such 
as  are  needed. 

One  of  the  simplest  of  the  common  form,  of  lever  safety- 
valve  is  that  seen  in  Fig.  83,  in 
which  the  valve,  A,  is  held  down 
to  its  seat  by  a  lever,  BC,  having 
a  fulcrum  at  the  pin,  C,  and  resting 
on  the  valve  at  D.  The  weight, 
W,  can  be  adjusted  at  any  distance 

from     D    that     may    give     the     mo-  FIG.  83.— LEVER  SAFETY-VALVE. 

ment  required  to  resist  the  intended  steam-pressure.  A  guide 
at  E,  secured,  like  the  pivot  standard  F,  to  the  valve-chamber, 
G,  keeps  the  lever  in  the  designed  vertical  plane.  The  size  of 
the  valve  is  usually  reckoned  as  that  of  the  opening,  //,  of 
pipe  and  valve-seat.  A  "  feather"  on  the  outer  side  of  the 
valve  guides  it  and  ensures  its  return  fairly  upon  its  seat  when 
it  falls  with  reduction  of  pressure.  Fig.  84  shows  the  exterior 
of  a  better  and  more  recent  type  of  lever  safety-valve.  In 
some  cases  weights  are  carried  directly  on  the  top  of  the  valve- 


388 


THE    STEAM-BOILER. 


stem,  a  spindle  rising  from  the  latter  over  which  they  are 
threaded ;  the  pressure  is  then  determined  by  adding  or  re- 
moving weights.  In  other  instances  the  weights  are  suspended 
below  the  valve  and  inside  the  boiler,  the  idea  being  to  make 


FIG.  84. — SAFETY-VALVE. 


them  inaccessible  to  any  one,  except  at  times  when  no  steam  is 
on  and  when  the  inspector  may  adjust  them.  Often  valves  are 
so  constructed  that,  once  adjusted,  they  may  be  locked  up,  and 
thus  made  safe  against  the  tampering  of  irresponsible  or  mali- 
cious persons. 


-40*  TO  POINT   OF  SUSPENSION    OF  WEIGHT 


FIG.  85. — RECENT  TYPE  OF  LEVER  SAFETY-VALVE  WITH  KNIFE-EDGES. 

A  better  form  of  lever  safety-valve  than  that  just  described 
is  that  proposed  by  the  U.  S.  inspectors,  Fig.  85,  in  which 
the  contacts  of  valve  and  fulcrum  with  the  lever  are  made  by 
knife-edges,  a  system  found  to  have  marked  superiority  over 


DESIGNING  ACCESSORIES— SETTING— CHIMNEYS.       389 

the  usual  pin-construction.  The  valve  is  commonly  covered 
by  a  "  bonnet,"  and  the  steam  flowing  past  the  valve  into  the 
chamber  so  made  is  conducted  away  by  an  attached  steam- 
pipe. 

The  proportions  adopted  by  the   Board  submitting  it*  are 
as  follows: 


AREA  OF  VALVES  EXPRESSED 

IN  SQUARE  INCHES. 

5". 

10". 

15". 

20". 

35". 

3O". 

Diameter  of  opening..  . 
Diameter  of  valves  .  .  . 
Length  of  lever.  .  .  . 

2.525 
2.76 

2C. 

3-37 
3  77 
^o. 

4-371 

4.58 
ac  . 

5-047 
5-23 

4O 

5.642 

5-S6 

1C 

6.781 
6-375 

47    ^ 

Distance  of  fulcrum.  .  . 
Angle  of  valve's  face.  . 
Width  of  face  
Length  of  fulcrum  link. 

21s° 

•15 

4-5 

%5- 

•  15 
45 

3-5 
45° 

.12 

4-5 

4- 

45° 
.17 

4-5 

4-5 
45° 
•17 
4-5 

4-75 

45° 
•15 
4-5 

When  well  proportioned  and  well  made,  these  valves  may 
be  expected  to  keep  the  steam  under  usual  conditions  within 


FIG.  86.— LEVER  SAFETY-VALVE  (U.  S.  BOARD  OF  INSPECTORS). 

one  or  two  per  cent  of  its  working  pressure ;  but  the  smaller 
valves  are  less  exact  than  the  larger  sizes. 


*  Report  on  Safety-valve  Test.     Washington,  1877. 


390  THE   STEAM-BOILER. 

The  essential  requirements  are  considered  to  be — 

(1)  Capability  of  discharging  any  excess  of  steam   above  a 
fixed  working  pressure. 

(2)  A  minimum  limit  of  variation  of  pressure  within  which 
the  valve  will  open  and  close. 

(3)  Uniformity  of  action  at  different  pressures. 

(4)  Reliability  of  action  under  continued  use. 

(5)  Simplicity. 

The  form  of  valve  just  described  meets  these  demands  in  a 
very  satisfactory  manner.  The  working  drawings  are  seen  in 
Fig.  86. 

The  effective  area  of  opening,  a,  required  to  discharge  a 
given  weight  of  steam,  w,  per  hour  was  found  to  be,  at  various 
usual  pressures,  as  follows : 


2  atmos. ,    30  pounds  per  square  inch a  =  w  X  0.0009 

4  atmos.,    60  pounds  per  square  inch a  =  w  X  0.0006 

6  atmos.,    90  pounds  per  square  inch a  =  w  X  0.0003 

7  atmos. ,  100  pounds  per  square  inch a  =  w  X  0.0002 


The  proportion  a  =  o.oo$w  is  taken  as  giving  a  safe  area, 
the  factor  of  safety  for  the  usual  pressures  being  10,  and  greater 
as  the  pressures  increase. 

In  many  cases  the  lever  and  weight  are  too  cumber- 
some, or  otherwise  objectionable,  and  a  spring  is  used,  acting 
either  directly  on  the  valve  or  on  a  short  lever — a  common 
practice  with  both  locomotive  and  marine  boilers.  Nearly 
all  the  later  forms  of  valve  are  of  the  former  of  these  two 
classes. 

It  is  found  very  difficult  to  avoid  a  considerable  variation  of 
steam-pressure  with  the  common  form  of  valve,  as  it  is  not 
often  practicable  to  secure  the  full  lift  of  the  valve.  Owing  to 
a  peculiar  action  of  the  impinging  currents  of  steam,  it  is  rarely 
possible  to  obtain  a  rise  of  more  than  about  0.2  inch  (0.5  cm.) 
without  serious  excess  of  pressure,  especially  with  low  steam. 
Many  expedients  have  been  proposed  to  meet  this  difficulty, 
as,  for  example,  in  the  Rochow  valve  of  Fig.  87,  in  which  a 


DE  SIGNING  A  CCK  SSOR  IE  S—  SE  T  TING-  CHIMNE  VS.       3  9 1 


piston  is  attached  below  the  valve,  having  a  slight  excess  of 
area,  and  thus  continually  forcing  the  valve  upward  to  the 
limit  of  its  rise  until  the  pressure  is  relieved. 

A  system  now  becoming  very 
common,  and  giving  most  satisfac- 
tory results,  is  that  known  as  the 
"  reactionary"  valve,  of  which  a 
good  example  is  that  of  Ashcroft 
(Fig.  88),  in  which  the  current  issu- 
ing from  under  the  valve  is  de- 
flected by  a  curved  lip  or  flange 
in  such  manner  as  to  cause  a 
pressure  by  its  reaction  that  aids 
effectively  in  raising  the  valve. 
This  system  of  construction  is  in 
very  extended  use. 

When  well  designed,  they  open      FlG-  S/.-ROCHOW'S  SAFETY-VALVE. 
promptly  and  widely,  discharge  the  surplus  steam  quickly,  and 
seat  themselves  at  once,  thus  preventing  any  observable  varia- 
tion of  working  pressure. 

In  designing  safety-valves  care  is 
to  be  taken  to  secure  ample  area  of 
opening,  freedom  from  liability  to 
stick  or  failure  to  rise  fully,  and  to  see 
that  if  the  spindle  passes  through  a 
guide  the  bearing-surfaces  are  not 
liable  to  rust  fast.  It  is  usual  to  line 
the  opening,  and  to  cover  the  spindle 
with  brass.  Narrow  valve-seats  are 
advisable  to  secure  tightness  and 
free  working,  and  straight  steam- 
ways. 

The  mechanism  of  one  of  the 
reactionary"  safe- 
ty-valves is  seen  in  Fig.  89,  in  which  B  B  is  a  nickel  seat,  C  C, 
the  valve  of  which,  CC,  is  the  adjustable  ring  introduced  to 
secure  the  desired  reaction.  FF  is  the  spring  and  D  D  the 


FIG.  88.— ASHCROFT' s  (REACTIONARY) 

SPRING-LOADED  SAFETY-VALVE.        IYlOSt  rCCCllt  OI  the 


392 


THE   STEAM-BOILER. 


spindle,    the    one    bearing  against    the    fixed    cross-bar,    G  G, 
and  the  other  attached  to  it  firmly.     The  channel,  a  a,  turns 

the  issuing  current  back  into  the  verti- 
cal direction,  and  thus  makes  the  re- 
actionary effect  a  maximum. 

Brass  or  nickel  valves  and  seats  are 
free  from  the  liability  to  dangerous 
corrosion  that  characterizes  iron. 

The  maximum  intensity  of  pressure 
under  any  lever  safety-valve  is 


p  _ 


wl  -\-  I'w'  -\-  w"f 


FIG.  89.— RICHARDSON'S  SAFETY- 
VALVE. 


when  a  is  its  effective  area  ;  w,  iv' ,  w" , 
the  weight  applied,  that  of  the  lever  and  that  of  valve  ;  /  /',  the 
lengths  of  lever-arm  from  weight  to  fulcrum,  and  of  that  from 
centre  of  gravity  of  the  lever;  and /"the  distance  from  fulcrum 
to  centre  of  valve.  The  actual  value  of  a  may  vary  enormously 
.in  any  one  valve  having  a  wide  seat,  accordingly  as  it  is  tight 
or  leaking.  If  perfectly  tight,  the  valve  will  rise  when  an 
equilibrium  is  reached,  assuming  a  to  be  the  area  within  the 
inner  periphery  of  the  seat ;  it  will  drop  when  the  pressure  has 
fallen  so  far  that  an  equilibrium  may  be  established,  a  being 
measured  to  the  exterior  periphery.  If  leaking,  these  two 
areas  may  have  almost  any  apparent  relation.  The  narrower 
the  seat,  the  less  these  differences. 

For  large  boilers,  "  multiplex"  valves,  consisting  of  a  set  of 
two  or  more  in  one  casing,  are  often  used  in  preference  to  a 
single  large  valve. 

184.  The  Feed  Apparatus  for  steam-boilers  is  not  usually 
designed  by  the  engineer  furnishing  the  plans  for  boilers,  but  is 
purchased  of  makers  of  feed-pumps  or  of  "  injectors"  as  it  may 
be  needed.  Where  open  heaters  are  used,  in  which  the  feed  is 
heated  before  it  is  pumped,  the  injector  cannot,  as  a  rule,  be 
used  ;  but  a  large  slow-moving  pump,  placed  sufficiently  low  to 
fill  with  certainty  at  every  stroke,  should  be  employed.  A 


DESIGNING  A  CCESSORIES—  SE  TTING—CHIMNE  VS.       393 

pump  driven  by  belt  and  by  the  main  engine  is  more  economi- 
cal in  operation  than  a  steam-pump.  The  independence  of  the 
latter,  and  their  convenience  of  operation,  have  caused  their 
very  general  introduction  ;  and  they  are  commonly  kept  at 
hand  for  emergencies,  even  where  the  "power-pump"  is  used. 
With  a  closed  or  coil  heater  water  may  be  forced  by  the  feed- 
pump through  the  heating-coils  and  on  into  the  boiler.  In 
this  case,  either  pump  or  injector  may  be  used.  The  latter  is, 
in  this  case  the  more  economical,  as  no  loss  occurs  except  of 
heat  from  the  steam  and  water  pipes,  and  this  loss  may  be  ren- 
dered insignificant  by  carefully  covering  them.  Even  the 
effect  of  friction  is  to  give  a  fully  compensating  increase  of 
temperature  to  the  water. 

The  steam-pumps  are  not  usually  economical  of  steam,  and 
often  use  ten  times  as  much  per  unit  of  work  done  as  good 
engines.  A  "  duty"  of  ten  millions  is  unusually  large. 

All  feed  apparatus  should  be  of  the  best  possible  construc- 
tion ;  should,  when  possible,  be  in  duplicate,  and  of  far  greater 
capacity  than  is  demanded  in  regular  work;  and  should  be 
placed  where  it  will  always  be  promptly  and  readily  accessible, 
and  kept  in  perfect  order.  Failure  to  act  promptly  and  effec- 
tively in  an  emergency  may  lead  to  incalculable  disaster.  In 
many  cases  injectors  are  used  in  ordinary  work,  and  very  large 
steam-pumps  kept  in  readiness  for  emergencies. 

Heating  the  feed-water  by  means  of  the  waste  gases  is  al- 
ways advisable  if  at  all  practicable,  as  well  as  the  utilization  of 
the  heat  of  all  exhaust-steam  from  engines  and  pumps  and  re- 
turns from  systems  of  heating-pipe. 

The  table  on  page  394  gives  the  percentage  of  saving  ef- 
fected by  heating  the  feed-water  of  a  steam-boiler  by  means 
of  heat  otherwise  wasted. 

185.  Minor  Accessories  and  details,  such  as  the  kind  and 
location  of  steam  and  water  gauges,  dampers,  automatic  con- 
trolling devices,  etc.,  should  be  as  carefully  considered  by  the 
designer  of  the  steam-boiler  as  any  other  parts  of  his  work. 

The  Steam-gauge  is  selected  from  among  the  numerous 
styles  and  makes  in  the  market,  and  is  never  designed  by  the 
engineer  preparing  plans  of  boilers.  The  most  common  form 


394 


THE   STEAM-BOILER. 


is  the  Bourdon  Spring  Pressure-gauge  (Fig.  90),  of  which  a 
number  of  modifications  are  in  use.  The  case,  A  A,  encloses 
a  coil  of  flattened  tube,  B  B,  closed  at  the 
free  end  and  open  to  boiler-steam  at  the 
supported  extremity.  As  the  pressure  rises 
and  falls,  a  tendency  to  expand  the  tube 
into  circular  section  produces  greater  or  less 
H^HBW  effect,  and  the  tube,  as  a  whole,  assumes  a 
greater  or  a  smaller  radius  of  curvature, 
throwing  its  free  end  one  way  or  the  other 
in  such  manner  as  to  measure,  by  the  trav- 
erse of  the  attached  pointer,  the  pressure  at 
FIG.  QO.-BOURDON  GAUGE.  each  moment,  of  the  confined  fluid.  Some- 
times the  tube  is  held  at  its  middle  point,  both  ends  being 
free,  and  their  relative  motion  affecting  the  pointer.  The 
more  stable  the  tube  and  the  more  reliable  the  mechanism 
connecting  it  with  the  hand  at  the  dial,  the  better  the  gauge. 

SAVING  BY  HEATING  FEED-WATER. 

(Steam  at  60  Ibs.) 


E 

nfi 

INITIAL  TEMPERATURE  OF  WATER  (FAHR.). 

EI* 

OJ 

32° 

40° 

50° 

60° 

70° 

80° 

9o« 

100° 

I20» 

140° 

1  60° 

180° 

200» 

H 

60° 

2.39 

I.7I 

0.86 

O 

80 

4.09 

3-43 

2  59 

i-74 

o  88 

0 

100 

5-79 

5.14 

4-32 

3-49 

2.64 

1.77 

0.90 

0 

120 

7-5° 

6.85 

6.05 

5-23 

4.40 

3-55 

2.68 

1.  80 

0 

140 

9.20 

8-57 

7-77 

6.97 

6.15 

S-S2 

4-47 

3.61 

1.84 

o 

160 

10.90 

o  28 

9-5° 

8.72 

7.91 

7.09 

6.26 

5-42 

3.67 

1.87 

0 

1  80 

I2.6o  1      2.OO 

11.23 

10  46 

9.68 

8.87 

8.06 

7-23 

5-52 

3-75 

i  91 

o 

200 

14-3°      3-71 

13.00 

12.20 

"•43 

10.65 

9-85 

9-03 

7.36 

5-62 

3-82 

1.96 

0 

220 

16.00  i    5.42 

14.70 

14.00 

I3-I9 

I2-33 

ii  .64 

10.84 

9.20 

7-50 

5-73 

3-93 

1.98 

240 

17-791    7-13 

16.42 

15.69 

14.96 

14.20 

13-43 

12.65 

11.05 

9-37 

7.64 

5-9° 

3  97 

260 

19.40  !      8.85 

18.15 

17-44 

16.71 

T5-97 

15.22 

14-45 

11.88 

11.24 

9-56 

7.86 

5-96 

280 

21.10 

20.56 

19.87 

I9.l8 

18.47 

17-75 

17.01 

16.26 

14.72 

13.02 

11.46 

9-73 

7-94 

300 

22.88 

22.27 

21  .6l 

20.92 

20    23 

19.52 

18.81 

18.07 

16.49 

14.99 

13-37 

11.70 

9-93 

Fig.  91    represents  a  section  of  the  Bourdon  tube.     The 
major  axis  is  placed  vertically  to  the  plane  of  the  coil.     Were 
it  placed  parallel  to  that  plane,  internal  pressure    ^^^^ 
would  close  up  the  coil  instead  of,  as  in  the  usual          IG.  9i. 
case,  uncoiling  it.     This  latter  is  the  disposition  adopted  by 
the  Author,  as  in  Fig.  92,  in  a  gauge  devised  by  him  for  very 


DESIGNING  ACCESSORIES— SETTING— CHIMNEYS.        39  5 


high  pressures,  and  especially  to  work  steadily  where  exposed  to 
heavy  jar,  as  on  locomotives. 

A  pair  of  corrugated  disks,  secured  together  at  the  edges, 
and  receiving  steam-pressure  within,  is  a  form  of  pressure-gauge 
spring  which  has  been  found  useful,  and  many  gauges  are  thus 
constructed.  All  spring  gauges,  unless  constructed  with  ex- 
traordinary care,  are  very  liable  to  give  after  a  time  misleading 
indications,  and  they  should  be  occasionally  tested  to  ascertain 
to  what  pressures  the  readings  on  the  dial  actually  correspond. 


I 


Fig.  84 

THURSTON'S  HIGH-PRESSURE  GAUGE 


FIG.  92. — THURSTON'S  HIGH-PRESSURE  GAUGE. 

Mercury-gauges,  in  which  the  pressure  is  measured  by  the 
height  of  a  mercury  column  balancing  it,  are  much  safer  than 
spring-gauges,  but  are  too  cumbersome  for  common  use.  All 
other  steam-gauges  are,  however,  referred  to  the  mercury-gauge 
in  standardizing  them. 


THE   STEAM-BOILER. 

Steam-gauge  connections  should  be  so  made  that  the  in- 
strument may  not  be  liable  to  injury  by  heat,  either  externally 
or  internally,  and  so  that  the  spring  shall  always  have  a  body 
of  comparatively  cold  water  interposed  between  itself  and  the 
steam.  A  coil  or  siphon-shaped  bend  in  the  gauge-pipe  is  gen- 
erally introduced  with  this  purpose  in  view :  it  fills  up  with  a 
body  of  water  condensed  from  the  steam  which  protects  the 
spring  from  injury  by  exposure  to  heat.  The  point  of  entrance 
of  the  gauge-pipe  into  the  boiler  is  simply  a  matter  of  conven- 
ience, usually. 

Gauge-cocks  and  water-gauges  should  be  set  where  they  will 
not  be  affected  by  any  foaming  that  may  occur  within  the 
boiler;  they  should  be  as  far  from  the  furnace  as  is  conven- 
ient, or  their  connections  should  be  led  to  a  quiet  part  of  the 
boiler.  A  foaming  boiler,  by  deceiving  the  eye  at  the  gauges, 
may  discharge  a  dangerously  large  amount  of  water  undetected. 
The  Low-water  Detector  and  Alarm  is  an  apparatus  which  is 
in  very  common  use  to  give  warning  should  the  water-level 
ever  fall  below  that  considered  safe.  It  com- 
monly consists  of  a  vertical  tube  closed  at  the 
top  by  a  fusible  plug,  or  by  a  valve  actuated 
by  a  rod  having  a  different  coefficient  of  ex- 
pansion from  the  tube  itself.  The  tube  com- 
municates at  the  lower  end  with  the  water- 
space  of  the  boiler.  It  ordinarily  stands  full  of 
water;  but  should  the  water-level  fall  below 
its  lower  end,  steam  displaces  the  water  in  the 
tube,  the  fusible  plug  melts,  or  the  valve  is 

FIG.  93. — LOW-WATER  ii.ii-rr  •  •  r^u 

ALARM.  opened  by  the  difference  in  expansion  of  the 

tube  and  rod,  and  steam  at  once  issues,  giving  warning  of  dan- 
ger. The  upper  end  of  the  tube  is  commonly  fitted  with  a 
steam-whistle,  the  blowing  of  which  when  the  steam  makes  its 
exit  insures  attention. 

Many  forms  of  grate-bars  are  used  in  steam-boiler  furnaces, 
some  of  which  are  provided  with  interlocking  devices  so  con- 
trived that  all  are  so  bound  together  that  it  is  impossible  for 
single  bars  to  warp  and  twist  out  of  shape  to  such  an  extent 
that  they  will  be  liable  to  burn.  In  other  cases  the  bars  are 
fitted  so  as  to  be  all  capable  of  vibration  or  rotation  by  the  ac- 


DESIGNING  ACCESSORIES— SETTING— CHIMNEYS.        3Q/ 

tion  of  a  single  handle,  and  thus  to  permit  convenient  cleaning 
of  the  fires.  Such  grates  are  in  very  common  use  in  anthracite- 
burning  furnaces. 

Fusible  plugs  are  inserted  at  convenient  points  in  plates  lia- 
ble to  be  the  first  to  be  left  dry  on  the  falling  of  the  water- 
level.  A  leaden  rivet  in  an  upper  seam  or  in  a  rivet-hole 
made  for  the  purpose  at  the  highest  part  of  a  crown-sheet  is 
often  relied  upon  ;  but  it  is  better  to  use  an  alloy  of  lower 
melting-point,  and  to  make  it  quite  large.  Several  small  plugs 
are  sometimes  inserted  in  a  larger  plug  of  cast-iron  properly 
located,  the  idea  being  to  thus  secure  greater  safety  by  avoid- 
ing the  chance  of  a  single  one  failing  to  serve  its  purpose.  A 
large  plug  of  fusible  metal,  projecting  well  above  the  crown- 
sheet  or  other  plate  in  which  it  may  be  placed,  and  having  a 
central  rod  of  copper  passing  completely  through  it  and  pro- 
jecting at  top  and  bottom,  is  a  very  excellent  device.  When 
its  upper  end  becomes  exposed  the  copper  rod  melts  out  of  its 
casing  and  falls  down  out  of  the  way,  exposing  clean  surfaces  of 
fusible  metal,  which  in  turn  melt,  and  the  purpose  of  the  appa- 
ratus is  accomplished  with  certainty.  In  some  cases  alloys  are 
so  altered  by  long  exposure  to  heat  that  they  fail  to  melt  when 
the  emergency  arises.  It  is  advised  by  the  best  engineers  that 
they  be  renewed  frequently.  An  accumulation  of  sediment  or 
scale  sometimes  prevents  their  working,  or  may  permit  their 
melting  without  causing  egress  of  steam  and  water,  as  is  usu- 
ally intended.  A  coating  of  thin  scale  will  often  sustain  all 
the  pressure  coming  upon  it  over  such  an  opening  as  is  left  by 
the  dropping  out  of  the  plug. 

The  best  fusible  plugs  consist,  as  a  rule,  of  an  outer  shell, 
as  in  the  figure,  filled  with  a  fusible  metal,  C,  in  the  form  of  a 
plug  extending  through  the  shell  from  top 
to  bottom.     The  shell  should    be  of    hard 
brass  to  insure  strength,  with  a  good  thread 
where  it  screws  into  the  plate,  and  a  good 
hexagonal  or  square  head,  and  durability  suf- 
ficient to  permit  several  fillings.    The  thread 
cut  in  the  shell  should  correspond  with  the 
gas-fitters'  standard.     The  use  of  such  plugs  FIG.  44.-FusiBLE  PLUG. 
is  often  required  by  law. 


39* 


THE   STEAM-BOILER. 


Low  temperatures  can  be  determined  by  the  melting-points 
of  compositions  of  lead,  tin,  and  bismuth ;  and  the  following 
may  be  used  for  fusible  plugs  :* 

An  alloy  of  i  part  lead,  i  part  tin,  4  parts  bismuth,  melts  at    94°    C.,   201°  F. 


Rose's  metal 


5 

3 

'      " 

8 

2 

4       "      3 

1      ' 

5 

I 

'       "      4 

'      ' 

5 

I 

'       "      i 

*      * 

i          (i         2 

' 

i 

I 

'       "      3 

'      ' 

'    .  . 

'       "      3 

1      ' 

i 

100 
IOO 

118.9 

141.2 

241 

167.7 

167.7 

200 


202 
2O2 
246 

257 
466 

334 
334 
392 


It  is  customary  to  use  such  compositions  in  making  "  fusi- 
ble plugs"  to  be  inserted  in  the  crown  sheets  or  tops  of  "  con- 
nections" liable  to  be  injured  by  low  water,  to  give  warning  of 
danger,  and  to  act  as  safety  devices  by  melting  when  uncovered 
and  permitting  steam  to  issue  into  the  furnace  and  flues. 

All  marine  boilers  subject  to  the  rules  of  the  United  States 
Treasury  Department  are  required  to  have  plugs  of  Banca  tin 
inserted,  of  not  less  than  0.5  diameter  in  the  smallest  part.f 
Cylinder  boilers  with  flues  must  have  one  in  each  flue,  and  one 
in  the  shell  not  less  than  four  feet  from  the  forward  end.  Fire- 
box boilers  must  have  a  plug  in  the  crown-sheet.  Upright  tu- 
bular boilers  must  have  a  plug  in  one  of  the  tubes,  two  inches 
or  more  below  the  lower  gauge-cock,  or  in  the  upper  tube- 
sheet  if  so  preferred  by  the  inspector. 

Where  manhole  covers  can  be  "  struck  up"  in  wrought-iron, 
as  many  of  them  are  now  often  made,  they 
are  much  safer,  as  well  as  lighter  and  more 
convenient  of  manipulation.  The  accom- 
panying figure  illustrates  such  a  construc- 
tion as  introduced  some  years  ago.  The 
two  guards  and  bolts  give  greatly  increased 
security  as  compared  with  the  ordinary  ar- 
rangement of  a  single  guard  and  bolt  at  the 
middle  of  the  cover. 

The    M'Neil   manhole  cover  and  guard 
represent    good    recent    practice,    as    seen 


FIG. 


5. — WROUGHT-IRON     .       .„.  .,        r^.  .  .  ,       ,  in 

PLATE.       in  r  ig.  90.      I  he  opening  througn  the  shell 


Weisbach. 


f  Regulations,  §  22. 


DESIGNING  ACCESSORIES— SETTING— CHIMNEYS.        399 

is  strengthened  by  a  wrought-iron  "  struck-up"  ring,  the 
section  of  which  is  L-shaped.  The  inner  edge  is  faced  to  re- 
ceive the  faced  bearing-surface  of  the  cover,  and  thus  makes  a 
steam-tight  joint  without  requiring  packing. 


FIG.  96. — M'NEIL  MANHOLE  COVER. 

The  "  blow-off  cock,"  which  controls  the  discharge  of  water 
through  the  "  blow-off"  pipe,  should  never  have  a  valve  substi- 
tuted for  it,  but  only  a  good  conical  cock  should  be  used.  It 
should  be  of  the  best  of  brass  or  bronze,  and  of  extra  strength. 
A  valve  is  liable  to  be  caused  to  leak  by  the  catching  of  dirt 
or  of  chips  between  it  and  its  seat,  and  thus  to  endanger  the 
boiler  by  undetected  leakage.  With  the  cock  no  uncertainty 
can  exist  in  regard  to  its  being  open  or  closed,  and  foreign 
matter  caught  by  the  plug  will  be  cut  off,  or  the  cock  will  be 
opened  an  instant  to  wash  it  away.  A  "  T  "  placed  outside  the 
cock  and  so  arranged  that  the  plug  can  be  taken  out  to  see 
whether  the  blow-cock  leaks,  and  if  so  how  much,  will  be 
found  an  important  element  of  security. 

The  "  feed-valve"  which  controls  the  introduction  of  the 
feed-water  into  the  boiler  should  always  be  a  strong,  well-made 
brass  valve,  of  the  best  of  metal  and  heavier  than  the  customary 
market  valves.  The  ordinary  steam-fitter's  valve  and  other 
brass-work  is  usually  much  too  light,  and  it  is  often  thought 
wise  to  make  special  patterns  for  boiler  connections.  The 
valve  should  be  placed  close  to  the  boiler  and  the  check-valve 
outside,  and  as  near  it  as  possible.  Often  a  single  valve — 
a  "  screw-check" —  serves  both  purposes.  It  should  be  so 
placed  that  in  case  of  the  valve  getting  loose  it  may  not  pre- 
vent the  entrance  of  the  water  into  the  boiler. 


CHAPTER    X. 

CONSTRUCTION   OF   STEAM-BOILERS. 

186.  The  Methods  and  Processes  employed  in  the  shop 
in  the  construction  of  steam-boilers  are  usually  simple,  and  in- 
capable of  very  great  refinement.  The  boiler-maker  receives  a 
set  of  drawings  from  the  designing  engineer,  which  exhibit 
the  general  form  and  proportions  of  the  boiler,  and  complete 
representations  of  all  details. 

These  drawings  should  include  front  and  side  elevations, 
and  plan,  together  with  sections  taken  wherever  necessary  to 
exhibit  the  internal  arrangement  and  structure.  All  dimen- 
sions should  be  carefully  marked  on  each  sheet,  and  the  work- 
men instructed  to  "go  by  the  figures,"  as  attempts  to  measure 
by  scale  are  apt  to  lead  to  mistakes.  The  thickness  of  each 
sheet  should  be  indicated,  and  the  location,  form,  and  size  of 
every  opening  to  be  made  in  the  shop.  General  plans  are 
commonly  made  on  a  scale  of  from  T\  to  -J  full  size,  ac- 
cording to  circumstances ;  but  detail  drawings  are  often  all 
made  full  size. 

The  boiler-maker  often  reproduces  the  general  drawings,  as 
well  as  all  details,  full  size,  on  a  set  of  large  boards  provided 
for  the  purpose,  and,  measuring  all  parts  anew,  makes  sure 
that  the  originally  given  dimensions  are  all  right  and  consis- 
tent with  each  other.  The  location  of  each  sheet  and  its 
seams  being  thus  determinable,  the  dimensions  of  the  rectangu- 
lar, or  other  simple  form  of  sheet,  as  it  is  to  come  from  the 
mill,  are  ascertained,  and  if  not  in  stock,  the  iron  or  steel  is 
ordered.  Mills  will  usually  be  able  to  supply  sheets  cut  very 
exactly  to  the  ultimate  size  and  shape,  and  thus  save  great 
expense  in  cutting  and  fitting  in  the  shop.  Every  sheet  should 
be  ordered  as  exactly  as  to  size  as  possible,  and  the  grade 
and  quality  should  be  as  precisely  specified  in  the  order-list 
thus  made. 


CONSTRUCTION  OF   STEAM-BOILERS.  4OI 

All  special  sheets  should  be  exhibited  by  sketches  as  well 
as  by  figures,  and  in  arranging  their  location  and  dimensions 
care  is  taken  to  bring  just  as  few  seams  into  the  furnace  and 
to  expose  riveting  to  the  heated  gases  as  little  as  possible ; 
heavy  laps,  two,  three,  or  even  more  sheets  coming  together 
in  the  joint,  as  is  sometimes  the  case,  are  very  apt  to  make 
trouble.  Laps  should  be  so  planned,  also,  as  to  be  easily 
reached  for  chipping  and  calking  when  necessary.  The  larger 
the  sheets,  generally,  the  better. 

The  order  being  filled,  the  work  of  construction  is  begun. 

187.  The  Apparatus,  Tools,  and  Machinery  employed 
in  boiler-making  are  of  the  simplest  character  ;  although  the 
tendency  is  constantly  observed  to  introduce  more  machine- 
work  to  the  exclusion  of  hand-work,  and  to  make  steam-boiler 
construction,  like  iron-bridge  construction,  approximate  more 
and  more  to  the  art  of  the  machinist.  The  boiler-maker  is 
coming  to  work  more  and  more  to  gauges  and  standards,  and 
the  boiler  is  getting  to  be  more  and  more  a  machine-made 
product. 

The  apparatus  used  in  taking  off  the  dimensions  from  the 
working  drawings  and  laying  them  down  on  the  sheet  consists 
of  a  set  of  rules,  scales,  straight-edges,  and  templates.  The 
latter  are  usually  strips  or  frames,  which  may  be  laid  down  on 
the  sheet,  and  which  contain  carefully  spaced  holes  correspond- 
ing to  the  rivet-holes  to  be  made,  in  number,  size,  and  loca- 
tion ;  they  permit  the  location  of  the  rivet-holes  with  accuracy 
and  dispatch.  , 

The  tools  employed  in  boiler-making  consist  of  tongs  with 
which  to  handle  hot  rivets  ;  riveting-hammers,  especially  de- 
signed for  their  work  ;  chipping  chisels  for  use  in  trimming  the 
edges  of  plates ;  cape-chisels  with  narrow  cutting  edges  for 
cutting  off  portions  of  the  sheet,  or  making  openings  in  it ; 
and  hammers  for  driving  these  chisels.  Drift-pins — tapering 
iron  pins  which  are  inserted  in  the  rivet-holes  to  draw  them 
into  line — are  also  used,  sometimes  endangering  the  construc- 
tion ;  calking  tools  are  used  for  making  seams  tight,  and 
"  expanders"  to  "  set"  tubes. 

The  machinery  of  the  boiler-maker  consists  of  heavy  rolls 
26 


4O2  THE   STEAM-BOILER, 

for  giving  the  sheets  the  cylindrical  form  ;  shears  for  cutting 
them  to  correct  outline ;  punches  for  making  rivet-holes  ; 
boring-lathes  or  drill-presses  for  making  the  large  holes  in  tube 
or  flue  sheets  ;  and  riveting-machines.  Where  large  boilers,  to 
carry  high  pressure,  and  therefore  made  of  heavy  plates,  are 
to  be  built,  all  these  tools  must  be  very  heavy  and  powerful. 
Reamers,  or  "  rimmers,"  are  used  to  enlarge  holes  found  to  be 
too  small  for  their  purpose.  In  the  best-equipped  establish- 
ments a  planer  is  used  to  give  the  edges  of  heavy  plates  their 
bevel,  and  that  exactness  of  line  that  is  essential  to  neatness  of 
appearance  along  the  lap,  as  well  as  to  secure  immunity  from 
injury  by  the  chisel  when  the  edge  of  the  lap  is  chipped  in  the 
older  way,  preparatory  to  calking. 

Various  kinds  of  rivet-heating  furnaces  complete  this  list 
of  apparatus  of  the  boiler-shop.  All  such  machinery  should  be 
very  substantial  and  powerful,  as  it  is  always  liable  to  be  sub- 
jected to  very  heavy  stresses. 

188.  Shearing,  Planing,  and  Shaping  the  sheets  to  the 
prescribed    size    and    form  are  operations   preliminary  to  the 
fitting  together  and  riveting  up  of  the  work. 

Shearing  is  performed  by  the  "  shears"  or  shearing-machine, 
which  consists  of  a  pair  of  strong  jaws,  of  which  the  one  is 
fixed,  the  other  movable,  and  actuated  by  a  powerful  toggle- 
joint  or  by  an  eccentric.  The  cutting  edges  are  usually 
straight,  but  set  at  a  slight  inclination  the  one  with  the  other, 
in  such  manner  that  the  cut  begins  at  one  end  of  the  blade 
and  runs  across  to  the  other,  thus  enormously  reducing  the 
force  required  to  effect  it.  This  operation  is  rapid  and  inex- 
pensive, but  is  liable  to  injure  the  metal  near  the  cut  if  it  is 
hard,  and  usually  leaves  so  rough  an  edge  that  it  is  advisable 
to  give  a  better  finish  by  means  of  the  planer.  Sharply  curved 
and  irregular  outlines  cannot  be  given  by  the  shears  or  the 
planer,  and  are  formed  by  the  chisel.  Occasionally,  the  rough 
work  is  done  by  drilling  a  series  of  holes  along  the  line  to  be 
cut,  and  dressing  out  to  the  line  with  the  chisel. 

189.  Flanging   sheets  which    are   to    receive   the   ends    of 
flues,  or  are  to  be  used  as  heads  and   riveted   to  the  shell,  is 
performed  at  open  fires,  by  means  of  which  an  even  heat  is  ob- 


CONSTRUCTION  OF  STEAM-BOILERS.  403 

tained  over  the  whole  area  to  be  worked,  and  the  flange  is  then 
made  by  hammering  the  edge  to  be  turned,  over  an  anvil  or 
properly  shaped  "  former."  In  some  cases,  when  considerable 
numbers  of  circular  or  other  simple  forms  are  to  be  flanged, 
flanging-machines  are  used,  in  which  the  whole  flange  is  formed 
at  one  operation,  the  disk  being  forced  by  hydraulic  pressure 
into  a  die  which  turns  up  the  flange  all  around.  In  some 
cases  dome-tops,  manhole-rings,  manhole-plates,  and  other 
parts  are  similarly  "  struck  up." 

Punching  and  drilling  are  performed  by  machinery  usually, 
and  for  the  latter  process  the  gang-drill  is  often  found  an 
economical  machine  :  it  consists  of  a  collection  of  drills  so  set 
as  to  be  driven  together,  and  so  to  make  a  number  of  holes 
at  once.  Punching  is  generally  practised  with  very  soft  steels, 
and  with  all  iron  ;  but  drilling  is  always  preferable  where  steel 
is  employed  of  appreciably  greater  hardness  than  good  iron, 
and  is  probably  safest  with  hard  irons. 

A  good  rule  in  working  steel  plate  is  to  punch  the  holes 
T3g-  inch  (0.476  cm.)  smaller  than  the  size  of  rivet,  and  then  to 
enlarge  the  hole  to  full  size  by  either  counterboring  or  ream- 
ing. The  sharp  edge,  or  fin,  if  any,  around  the  hole  should 
finally  be  trimmed  so  as  to  make  a  slightly  rounded  fillet  under 
the  head  of  the  rivet,  and  thus  reduce  the  risk  of  fracture  at 
that  point. 

For  these  operations  the  holes  have  been  previously  marked 
off  by  the  template,  and  the  art  of  successfully  doing  the  work 
is  mainly  that  of  securing  exact  location  of  the  punch  or  drill 
at  starting.  A  table,  carrying  the  plate  and  moving  automati- 
cally the  correct  distance  to  give  the  desired  spacing  at  each 
operation,  is  often  adopted,  and  with  advantage.  When  punch- 
ing, the  sheet  should  be  so  placed  that  the  side  at  which  the 
punch  enters  shall  be  that  next  the  adjacent  sheet  when 
riveted  up,  thus  producing  a  hole  for  the  rivet  largest  on  the 
outside,  next  the  heads,  and  smallest  at  the  middle. 

190.  Bending  Plates  to  the  required  curvature  is  often 
the  first  process,  though  frequently  performed  after  the  opera- 
tions just  described  are  completed.  The  bending  rolls  are  so 
set  as  to  produce  a  moderate  degree  of  curvature  at  the  first 


404  THE   STEAM-BOILER. 

passage  of  the  plate,  and  repeatedly  adjusting  the  rolls  and 
successive  passes  of 'the  sheet  finally  give  the  full  curvature 
desired.  Where  the  shape  to  be  secured  is  the  frustum  of  a 
cone,  one  end  of  the  sheet  is  more  closely  pressed  in  the  rolls 
than  the  other,  and  a  sharper  curvature  given  it.  The  use  of 
a  template  determines  when  the  plate  has  the  right  curvature. 

191.  Riveting  is  done  partly  on  detached  portions  of  the 
boiler,  as  in  making  flues  and  fireboxes,  and  partly  in  assem- 
bling such  parts  and  building  up  the  complete  structure.  As 
a  rule,  all  parts  which  can  be  easily  handled  are  completed 
separately,  and  later  joined  to  adjacent  parts  in  the  final  work 
of  putting  them  all  together.  Each  member  being  compara- 
tively light  and  small,  the  work  can  be  done  on  it,  detached, 
much  more  conveniently,  rapidly,  and  cheaply  than  when  it  is 
attempted  to  construct  it  as  an  attached  portion  of  the  larger 
mass. 

Before  riveting  up,  each  scam  is  examined  to  see  that  the 
two  halves  of  the  lap  are  precisely  matched,  the  edges  parallel 
and  well  adjusted,  and  opposite  rivet-holes  all  exactly  located 
and  fair  with  each  other.  Should  any  fault  appear  it  is  cor- 
rected before  riveting  is  begun.  While  making  this  trial  of 
parts  and  doing  this  fitting,  and  while  making  this  examina- 
tion, the  seam  is  temporarily  held  by  bolts  which  should  nearly 
fit  the  holes  intended  for  the  rivets.  Should  a  pair  of  rivet- 
holes  be  unfair,  the  bolt  will  not  enter,  and  one  or  both  the 
holes  must  be  dressed  over  with  a  reamer  until  the  rivet  can 
enter.  The  drift-pin  is  used  to  bring  companion  sets  of  holes 
opposite,  when  in  doing  this  the  plate  requires  to  be  slightly 
sprung ;  but  it  ought  never  to  be  employed  to  enlarge  the 
holes  or  to  force  them  fair  by  visibly  distorting  the  sheet  or 
the  metal  about  the  hole.  When  this  process  seems  necessary, 
and  when  enlargement  by  chipping  produces  a  seriously  mis- 
shapen hole,  the  faulty  sheet,  or  pair  of  sheets,  should  both  be 
in  fault,  should  be  condemned,  and  better  prepared  sheets 
substituted. 

When  the  seam  is  found  to  be  right,  the  two  edges  are 
bolted  firmly  in  position,  with  the  laps  in  perfect  contact,  and 
riveting  proceeded  with.  Every  rivet  should  be  of  the  length 


CONSTRUCTION  OF  STEAM-BOILERS.  405 

and  size  required  by  specification,  and  of  the  best  material.  In 
heating,  the  shank  is  given  a  good  forging  temperature,  the 
head  left  barely  red,  and  the  point  safely  inside  the  burning 
heat.  A  few  blows  on  the  laps,  with  the  rivet  in  place,  deter- 
mine whether  metallic  contact  exists,  and  the  rivet  is  then 
rapidly  headed  up  and  shaped.  Quick  work  means  easy  and 
good  work,  as  the  riveting  is  then  finished  before  the  rivet  is 
hardened  by  cooling.  Riveting-hammers  are  comparatively 
light ;  but  the  rivet  is  held  up  to  its  place  by  heavy  hammers, 


FIG.  97. — STEAM  RIVETING-MACHINE. 

weighing  from  ten  to  sometimes  thirty  or  forty  pounds  (4.5  to 
14  or  1 8  kgs.),  and  capable  by  their  inertia  of  resisting  the 
heaviest  blows  struck  during  the  operation.  Two  or  three 
hundred  blows  are  required  for  each  rivet  in  ordinary  boiler- 
work.  Very  heavy  rivets  are  headed  up  with  a  "  button-set," 
a  forming  tool  which  is  cup-shaped  at  one  end,  where  it  rests 
on  the  point  of  the  rivet,  while  blows  of  a  sledge-hammer 
on  its  other  end  drive  it  down  and  so  give  the  head  a  hemi- 
spherical shape.  This  form  of  head  is  stronger  than  the  cone- 
shape  usually  given  in  hand-riveting. 


406  THE   STEAM-BOILER. 

Machine-riveting,  either  by  steam,  compressed  air,  or  hy- 
draulic machines,  is,  if  well  done,  preferred  to  any  hand-rivet- 
ing ;  although  on  work  which  is  not  too  heavy  the  latter  is 
thoroughly  capable  of  giving  satisfaction.  In  machine-riveting 
the  machine  should  be  amply  powerful ;  the  die  should  be 
carefully  brought  in  line  with  the  rivet ;  the  laps  should  be 
very  closely  secured  together,  and  the  pressure  fully  up  to  the 
working  standard.  A  machine  which  will  clamp  and  hold  the 
lap  while  the  rivet  is  driven  is  to  be  preferred. 


FIG.  98.— HYDRAULIC  RIVETER. 

Well-constructed  steam-riveters  of  angular  size  do  their  work 
by  pressure,  not  by  impact  or  blow.  The  boiler-pressure  should 
be  varied  to  suit  the  size  of  the  rivets  being  driven,  and  main- 
tained at  a  uniform  pressure  during  the  entire  work.  A  good 
steam-riveter  should  drive  ordinary  sizes  of  rivets  ten  times  as 
rapidly  as  a  single  gang  of  riveters  working  by  hand,  notwith- 
standing the  time  and  labor  required  in  the  handling  and  ad- 
justment of  the  boiler,  the  rivet,  and  the  machine.  The  lighter 
machines  are  compelled  to  strike  a  blow :  this  gives  less  satis- 
factory and  far  less  reliable  work  than  when  the  machine  has 


CONSTRUCTION  OF  STEAM-BOILERS. 


407 


sufficient  power  to  head  up  the  rivet  by  steady  pressure.  In 
working  this  machine  the  rivets  are  inserted  from  the  outside 
of  the  boiler,  instead  of,  as  in  hand-riveting,  from  the  inside. 
The  boiler,  suspended  in  slings  attached  to  a  crane,  is  drawn 
up  to  the  riveting-hammer,  and  the  pressure  heads  up  the  rivet 
in  a  moment,  and  the  steam-pressure  is  retained  until  the  rivet 
is  cool.  The  charge  of  steam  used  in  riveting  is  sometimes 
utilized  in  its  expansion  to  draw  back  the  ram. 

\<d\ 


FIG.  99. 


FIG.  ioo. 


To  drive  rivets  by  hand,  two  strikers  and  one  helper  are 
needed  in  the  gang,  besides  the  boy  who  heats  and  passes  the 
rivets;  to  drive  each  f-inch  rivet  an  average  of  250  blows  of  the 
hammer  is  needed,  and  the  work  is  but  imperfectly  done. 
With  a  steam  riveting-machine,  two  men  handle  the  boiler  and 
one  man  works  the  machine. 


FIG.  101. 

Where  the  plates  of  which  portions  of  a  boiler  are  com- 
posed meet  at  right  angles,  the  connection  may  be  made  by 
either  of  the  methods  exhibited  in  the  illustrations  above:  as 
by  angle-iron  (Fig.  99)  ;  by  a  T-iron,  when  stiffness  is  desirable 
in  the  transverse  plane  (Fig.  ioo)  ;  or  by  flanging  (Fig.  101). 

In  order  to  exhibit  the  relative  advantages  of  machine  and 
hand  riveting,  we  have  in  Fig.  102  an  illustration  of  two  plates 


408  THE   STEAM-BOILER. 

riveted  together,  the  holes  of  which  were  purposely  made  so  as 
not  to  match  perfectly.  Rivet  a  was  put  in  by  the  steam-riveter, 
and  b  by  hand.  The  machine-rivet  fills  the  hole  completely, 
while  the  hand-rivet  is  very  imperfect. 

The  hand-rivets  fill  up  the  holes  immediately  under  the 
head  formed  by  the  hammer;  but  sufficient  pressure  could  not 
be  given  to  the  metal  by  hand  to  insure  equally  good  work. 

The  hydraulic  riveting-machine  compresses  without  a  blow, 
and  with  a  uniform  pressure,  variable  at  will ;  each  rivet  is 


FIG.  102.— HAND  AND  MACHINE  RIVETING.  FIG.  103.— ACCUMULATOR  AND  PUMP. 

driven  with  a  single  movement,  under  complete  control.  The 
pressure  upon  the  rivet  after  it  is  driven  is  maintained,  or  the 
die  is  retracted,  as  may  be  desired.  This  machine  consists  of 
a  riveting-die  attached  to  a  piston  in  the  compressing  cylinder ; 
this  cylinder  communicates  with  an  accumulator  through  a 
valve  moved  by  the  operator.  The  work  is  performed  without 
a  blow;  the  pressure  is  always  uniform,  and  can  be  adjusted  by 
the  weights  applied  to  the  accumulator;  it  may  be  maintained 
as  long  as  desired,  or  the  riveting-die  can  be  retracted  as  soon 
as  the  rivet  is  finished.  The  succeeding  diagrams  illustrate  this 
system.* 

*  Supplied  through  the  courtesy  of  Messrs.  Sellers  &  Co. 


CONSTRUCTION  OF  STEAM-BOILERS. 


409 


Cold-riveting  can  be  successfully  adopted  on  light  work  when 
the  best  material  can  be  obtained  in  the  rivets,  and  is  preferred 
where  choice  is  allowed  on  account  of  the  greater  certainty  in 
regard  to  quality  of  rivet  and  the  freedom  from  risk  of  injury 
by  heat. 

Steel  rivets  must  be  worked  more  rapidly  than  iron. 

The  accumulator  is  an  essential  part  of  the  system:  in  it 
water  is  kept  under  pressure  by  means  of  a  pump,  or  otherwise. 
The  chamber  of  the  accumulator  is  closed  at  one  end,  and  to 
the  other  end  is  fitted  a  stuffing-box  through  which  a  weighted 


FIG.  104. — HEAVY  LAP. 

plunger  rises  or  falls  as  the  quantity  of  water  in  the  chamber 
increases  or  diminishes.  By  varying  the  load  upon  the  plunger, 
the  pressure  upon  the  water  in  the  accumulator-cylinder  is  ad 
justed.  The  water  under  pressure  in  the  accumulator  is  there 
stored  ready  for  use,  and  is  conveyed  through  suitable  pipes  to 
the  compressing  cylinder  of  the  riveting-machine,  so  that  when 
the  valve  is  opened  the  water  flows  into  the  cylinder,  forcing 
the  riveting-dies  upon  the  rivet,  and  finishing  the  work  with 
such  force  as  the  accumulator  has  been  gauged  to  produce. 
The  very  high  pressure  at  which  hydraulic  machines  are 
operated,  as  compared  with  steam-riveters,  makes  the  cylinder 
smaller  and  the  machines  less  cumbersome.  The  hydraulic 
riveting-machine  can  be  used  wherever  power  by  belt  is  obtain- 
able, and  the  pumps  and  accumulator  may  be  placed  at  any 
point  most  convenient  for  the  application  of  the  power.  In 
bridge-  and  ship-building  the  portable  hydraulic  riveter  is  com- 
monly employed. 


THE   STEAM-BOILER. 


The  adjustment  of  laps  and  of  courses,  where  the  metal  is 
thick  and  construction  intricate,  often  demands  much  ingenuity 
on  the  part  of  either  the  designer  or  the  builder  of  the  boiler. 
Fig.  104  illustrates  the  usual  arrangement  in  the  shell  of  marine 
boilers  of  the  Scotch  type,  where,  as  is  customary,  butt  joints 
are  employed  with  double  riveting. 

The  following  sketches  illustrate  some  of  the  best  forms  of 
joint  in  standard  construction,  beginning  with  the  single-riveted 
joint  of  everyday  use,  and  followed  by  various  forms  of  double 
and  triple  riveting. 


SINGLE  RIVETED. 


) 


SINGLE  RIVETED  BUTT  JOINT. 
NOT  DESIGNED  FOR  STRENGTH, 

SCALE     1  =  4' 
ASSUME    T= 


FIG.  io5<». 


CONSTRUCTION  OF  STEAM-BOILERS. 


411 


These  joints  are  all  proportioned  as  for  steel,  and  a  strength 
is  assumed  of  5000  pounds  per  running  inch,  the  factor  of  safety 
being  taken  as  8,  or  for  8000  pounds  if  the  factor  be  dropped 
to  5. 

The  second  of  the  group  shows  the  junction  of  four  over- 
lapping plates;  and  the  third  the  method  of  arranging  the 
covering-strips  or  "  cover-plates." 


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Where,  as  should  always  be  the  case,  steel  plates  are  drilled, 
or  are  punched  and  the  holes  sufficiently  enlarged  by  counter- 
boring  or  reaming  and  the  plates  finally  well  annealed,  no  al- 


412 


THE   STEAM-BOILER. 


lowance  need  be  made  for  loss  of  strength   in   the   metal  be- 
tween the  plates. 

The  best  makers  of  boilers  endeavor  to  reduce  the  number 
of  seams  to  a  minimum,  as  well  as  to  make  those  retained  of 
uniform  and  ample  strength.  Double-riveted  longitudinal 
seams  are  becoming  constantly  more  common,  and  in  some 
cases  welding  is  resorted  to  with  great  success.  The  latter 
plan  permits  the  securing  of  perfectly  cylindrical  courses  or 
rings  of  plates.  It  seems  not  improbable  that  welding  may 
ultimately  become  the  usual  method  of  making  all  joints.  The 


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TRIPLE  RIVETED. 
ZIGZAG. 


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I- 


FIG.  io5<r. 

lap-joints  are  disappearing  in  good  designs,  and  the  butt-joints, 
single  and  double  riveted  or  other,  are  taking  their  place. 
In  these  cases  the  cover-plates,  or  covering  strips,  or  straps,  as 
they  are  variously  called,  should  be  cut  from  plate,  and  in  such 
manner  that  the  grain  shall  run  parallel  with  the  direction  of 
stress. 

Welding,  if  it  can  be  safely  relied  upon,  offers  so  many  ad- 
vantages over  riveting,  that  there  can  be  no  question  that  it  will 
in  time  supplant  entirely  the  older  method  of  uniting  the  parts 
of  boilers.  It  has  been  the  practice  of  a  few  makers  to  employ 
this  system  for  many  years,  and  the  use  of  welded  seams  is  slowly 
but  steadily  increasing.  A  good  weld  gives  more  nearly  the  full 


CONSTRUCTION   OF  STEAM-BOILERS.  413 

strength  of  the  iron  than  can  any  arrangement  of  rivets,  and  en- 
ables all  risks  arising  from  defects  in  workmanship  peculiar  to 
riveting,  such  as  drifting  or  careless  chipping  and  calking,  and 
such  as  cold-hammering,  to  be  avoided.  It  permits  dispens- 
ing with  calking  entirely,  and  consequently  the  avoidance  of  the 
grooving  or  furrowing  which  so  often  proves  dangerous.  It  is 
also  possible  to  reroll  the  course  or  ring  of  welded  plates,  and 
thus  to  secure  greater  accuracy  of  dimension  and  perfection  of 
form  than  could  be  obtained  with  riveted  work. 

Welding  is  less  likely  to  prove  unreliable  in  flues  than  in 
shells  of  boilers ;  as  the  steam-pressure  there  tends  to  force  the 
parts  together,  rather  than  to  separate  them,  as  in  the  latter 
case.  Great  experience  is  in  any  case  demanded,  as  well  as 
great  care  and  skill,  in  making  long  lines  of  weld,  such  as  are 
required  in  this  work.  It  is  stated  by  Mr.  Adamson,  who  has 
been  one  of  the  most  successful  makers  using  the  process,  that 
the  metal  must  be  of  the  best  possible  quality,  and  that  steel 
containing  enough  carbon  and  other  elements  to  perceptibly 
harden  it  cannot  be  safely  employed. 

192.  Flues  and  Tubes  are  set  after  the  parts  of  the  boiler 
are  assembled,  or  in  the  construction  of  the  tube-boxes  and 
"  connections."  The  flue  is  commonly  riveted  into  the  flanged 
opening  cut  into  the  two  flue-sheets  to  receive  it ;  the  tube  is 
"expanded"  into  the  tube-sheet  by  means  of  a  "tube- 
expander,"  of  which  there  are  many  kinds ;  which  tool  forces 
out  the  tube  into  metallic  and  firm  contact  with  the  hole  bored 
to  receive  it,  and  at  the  same  time  expands  it  a  trifle  on  each 
side  the  sheet,  and  thus  tightens  its  hold  and  gives  it  the 
effect  of  a  stay,  while  still  further  insuring  against  leakage. 
Care  must  be  taken  to  avoid  too  great  expansion,  as  the  tube- 
sheet  is  sometimes  strained  and  weakened  by  excessive  stretch- 
ing, and  the  tube  itself  is  sometimes  split.  Properly  set  and 
expanded,  a  tube  makes  an  exceedingly  effective  stay.  A 
locomotive  tube  should  safely  carry  3000  pounds  (1360  kgs.) 
and  a  marine  boiler  tube,  of  double  the  diameter,  5000  pounds, 
(2268  kgs.),  or  the  full  boiler-pressure  ordinarily  carried.  For 
very  high  pressures,  as  now  often  attained  with  three  and  four 
cylinder  "  compound  "  engines,  stay-tubes  are  introduced  at  in- 


THE   STEAM-BOILER. 


'    FIG.  106. — STAYING  FLAT  SURFACES. 


tervals  which  are  made  of  heavier  iron,  and  have  nuts  screwed 
on  the  outside  to  sustain  the  excessive  pressure.     Many  build- 


CONSTRUCTION  OF  STEAM-BOILERS.  415 

ers  prefer  not  to  bead  over  the  ends  of  the  tubes,  fearing  that 
the  operation  may  loosen  them  and  cause  leakage.  The  ends 
of  the  tubes  are  annealed  before  expanding  them. 

In  laying  out  the  flue  or  tube  sheets,  the  centres  are  located 
by  reference  to  the  drawings,  and  the  outline  of  the  hole  is  laid 
out  by  the  dividers.  For  flue-sheets,  a  row  of  small  holes  is 
drilled  around  the  circle,  marking  the  opening  to  be  made;  the 
centre  part  is  cut  out,  the  opening  trimmed  and  flanged,  and 
the  sheet  is  then  ready  to  receive  the  flue.  Tube-sheets  are 
similarly  laid  off,  a  small  hole  drilled  at  each  centre,  and  the 
hole  then  "  counterbored  "  to  the  required  size  and  the  edges 
of  the  enlarged  holes  smoothly  rounded  to  prevent  cutting  the 
tubes  when  expanded  in  place. 

Ferrules  are  often  driven  into  the  tube-ends,  partly  to  give 
greater  tightness,  partly  often  to  reduce  the  draught-area  when, 
as  sometimes  occurs,  it  is  too  great. 

Staying  is  variously  practised,  and  marine-boilers  especially 
exhibit  a  great  variety  of  methods.  Fig.  106  illustrates  a 
somewhat  peculiar  method  of  staying  adopted  in  the  boilers  of 
the  U.  S.  S.  Nipsic.  A  set  of  gusset-plates  is  riveted  to  the 
shell,  and  the  connection  is  stayed  to  them  by  means  of  lugs 
riveted  to  both.  The  long  stay-rods  running  lengthwise  of  the 
boiler  are  connected  to  these  gusset-plates.  Other  gusset-plates 
stiffen  the  junction  of  the  adjacent  parts  of  the  shell  above 
the  connection.  The  water-spaces  are  stayed  by  riveted  stay- 
bolts  in  the  usual  manner. 

Fig.  107  illustrates  the  staying  of  the  heads  of  the  boilers 
of  the  U.  S.  S.  Monadnock. 

Fig.  108  exhibits  the  method  of  staying  adopted  in  the 
boilers  of  the  U.  S.  S.  Miantonomoh,  which  differs  from  the 
more  common  practice  in  the  manner  of  fastening  the  heads  of 
the  stay-rods.  The  eyes  to  which  the  rods  are  attached  at 
the  end  are  made  fast  to  the  shell  by  means  of  bolts  passing 
through  the  plates  and  held  by  nuts  on  the  outside. 

The  usual  method  of  securing  the  stay-rods  and  "  crow- 
feet "  in  marine-boiler  construction  is  seen  in  Fig.  109,  as  prac- 
tised in  the  boilers  of  the  U.  S.  S.  Terror.*  A  set  of  i-irons  is 

*  Shock  on  Boilers. 


THE   S  TEA  M -BOILER. 


FIG.  107. — STAYING  FLAT  SURFACES. 


FIG.  108. — STAYING  FLAT  SURFACES. 


CONSTRUCTION  OF  STEAM-BOILERS. 


417 


riveted  on  the  inside  of  the  shell  which  gives  an  anchorage  for 
the  crow-feet  to  which  the  stay-rods  lead,  the  connections  being 
made  by  bolts  in  shear. 

Fig.  no  represents  the  method  of  staying  adopted  in  the 
boilers  of  the  S.S.  Lord  of  the  Isles  to  secure  the  heads. 

193.  Chipping  and  Calking  seams  after  they  are  riveted 
up  is  a  process  which  is  relied  upon  to  insure  against  leak- 
age. The  workman,  with  hammer  and  chisel  chips  the  edge 
of  the  lap  smoothly  from  end  to  end — sometimes  only  on  the 
outside,  but  often,  if  accessible,  on  the  inside,  and  thus  ob- 
taining a  smooth  edge ;  then  drives  a  blunt  "  calking-tool " 
against  it,  and  thus  expands  the  metal  against  the  opposite 
plate,  and  securing  metallic  contact  closes  every  leak. 


FIG.  109. — STAYING  FLAT  SVRFACES. 

The  process  of  chipping  is  a  dangerous  one,  and  the  score 
produced  by  the  chisel  as  its  corner  marks  the  under  sheet  has 
been  often  known  to  lead  to  the  formation  of  a  groove  or  a 
crack,  and  later  to  explosion.  Planing  the  edge  before  final 
assembling  and  riveting  up  is  much  to  be  preferred.  The  use 
of  the  calking-tool  has  sometimes  resulted  in  similar  injury; 
and  split-calking,  which  consists  in  driving  the  edge  of  a  chisel 
into  the  edge  of  the  sheet  and  thus  splitting  it  slightly  and  ex- 
panding the  lower  part  against  the  adjacent  sheet,  is  advised  as 
a  safer  plan.  The  Connery  system,  regarded  by  many  as  very 
much  better  than  either  of  the  preceding,  is  similar  to  the  last ; 
27 


4i8 


THE   STEAM-BOILER, 


but  a  round-nosed  tool  is  employed  which  makes  a  smooth, 
semi-cylindrical  groove  instead  of  a  sharp  crack.  The  expand- 
ing effect  is  also  felt  further  back  under  the  lap,  the  seam  is 
thus  tighter  and  more  permanently  so,  and  the  use  of  the  tool 
is  not  liable  to  injure  the  lower  sheet. 


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FIG.  i  to. — STAYING  FLAT  SURFACES. 

In  European  practice,  even  where  the  builders  have  not 
gone  so  far  as  to  adopt  the  system  of  calking  with  a  round- 
nosed  tool,  they  have  very  generally  substituted  for  the  old 
and  dangerous  form  of  calking-tool  a  wider-edged  tool  called 
the  fullering-tool,  and  the  specifications  usually  prescribe  ful- 
lered seams  as  well  as  planed  edges.  No  calking-tool  should 
ever  be  permitted  to  be  used  which  has  a  sharp  edge  or  corner 
that  may  by  careless  handling  be  made  to  cut,  or  even  mark, 
the  sheet  at  the  edge  of  the  lap. 


CONSTRUCTION  OF  STEAM-BOILERS.  419 

Butts  are  calked  with  a  tool  which  makes  a  depression  on 
each  side  the  line  of  junction,  expanding  the  two  sides  into 
contact  and  making  that  line  tight.  It  is  customary  with  some 
makers  to  calk  around  the  heads  of  rivets,  and  when  found 
leaking  this  process  is  resorted  to  as  a  remedy.  Calking  should 
not  be  done  while  the  boiler  is  under  pressure,  and  should  be 
very  carefully  done  at  all  times. 

The  "  concave"  calking,  so-called,  is  exhibited  in  the  ac- 
companying figure,  which  shows  the  difference  in  the  effect 
of  the  new  and  old  methods  upon  the  sheet.  The  plate  is 
shown,  as  bent  after  the  operation,  to  determine  the  extent  to 
which  injury  of  the  plate  may  have  been  incurred.  On  the  left 
is  seen  the  action  of  the  concave  system,  the  effect  of  the  tool 
being  somewhat  more  marked  than  is  customary,  but  perfectly 
representing  samples  in  possession  of  the  Author.  On  bending 


FIG.  in. — CONCAVE  AND  COMMON  CALKING. 

down  the  sheet,  as  shown,  it  is  seen  to  be  quite  sound,  and  en- 
tirely unaffected  by  the  action  of  the  tool.  On  the  other  hand, 
the  ordinary  tool,  as  commonly  used  and  as  illustrated  on  the 
right  in  the  same  engraving,  is  almost  invariably  found  to  pro- 
duce a  slight  indentation  of  the  sheet  along  the  edge  of  the  lap, 
and  then  to  cause  a  tendency  to  crack  when  the  sheet  is  flexed 
by  the  changing  temperatures  of  the  boiler  and  accompanying 
strains.  By  this  method  either  the  edge  of  the  tool  or  the 
edge  of  the  lap  is  liable  to  produce  a  dangerous  groove,  at 
ojice  or  after  corrosion  has  progressed  somewhat.  The  more 
rational  system  gives  a  broad  band  of  metallic  contact  between 
the  two  sheets,  and  makes  the  joint  tight  without  injury  to 
the  structure.* 

In  using    the   "  round-nosed "   calking  tool,   the   following 
directions  should  be  observed : 

*  Journal  Franklin  Institute,  1874. 


42O  THE   S  7^EA  M-B  OILER. 

Chip  or  plane  the  plates  to  an  angle  of  about  1 10°,  seeing 
that  the  seams  are  perfectly  close  inside  and  outside.  Apply 
the  tool  in  the  usual  manner,  forming  a  channel,  and  always 
keeping  the  burr  between  the  tool  and  plate,  and  calk  until 
found  solid,  smooth,  and  brought  to  a  feathered  edge,  free  from 
pin-holes.  Do  not  cut  off  the  burr,  as  it  may  injure  the  under 
plate.  Upon  testing,  if  pin-holes  are  found,  apply  the  same 
tool  as  before,  until  made  perfectly  tight.  The  convex  tool 
should  taper  about  two  inches  from  the  point,  which  is  about 
half  an  inch  wide,  otherwise  perfectly  straight,  save  when  un- 
avoidable, and  ground  to  a  radius  that  will  finish  the  concave 
channel  to  about  one  half  the  bevelled  edge  ;  if  too  wide  it  will 
thicken  the  edge ;  if  too  small  it  will  wedge  it  off. 

194.  Assembling  is  the  process  of  fitting,  and  finally  rivet- 
ing permanently  together,  all  the  details  and  members,  which, 
separately  constructed,  are  finally  brought  together  to  make  the 
complete  structure.     The  shell,  the  tubes  and  their  tube-sheets, 
with  the  front  and  back  connections  and  the  steam-drum,  are 
the  several  principal  parts  thus  dealt  with.     The   shell  is  first 
set  in  position  and  riveted  up ;  the  flues  or  tubes  and  connec- 
tions are  next  finished,  placed  in  their  proper  position  within 
the  shell,  and  riveted  into  place  ;  the  drum  or  dome  is  attached  ; 
and,  finally,  all  minor  details  are  added,  and  the  boiler  is  ready 
for  examination,  test,  and  finally  for  calking  and  "  finishing." 

195.  Inspection  of  the  work  should  take   place,  not  only 
when  the  boiler  is  reported  completed,  but  should  be  kept  up 
constantly    throughout    the    whole    period    of    construction. 
Where   extensive  contracts   are  filled,  it  is  usual   for  the  pur- 
chaser to  have  a  skilled  inspector  constantly  employed  to  see 
that  the  material  introduced  is  in  accordance  with  the  contract  ; 
that  the  construction   is  precisely  what   is   called   for  by  the 
drawings  and  specification,  the  work  well  done,  and  the  whole 
properly  put  together. 

A  special  inspection  is  usually  provided  for,  to  take  place  at 
completion  and  before  acceptance.  At  this  time  the  inspector 
very  carefully  and  minutely  examines  the  boiler  inside  and  out, 
overhauling  the  braces  and  stays,  their  connections  with  the 
shell  and  other  parts,  and  their  welds  and  fitted  parts  ;  he 
observes  the  character  of  the  riveting,  the  method  of  attach- 


CONSTRUCTION   OF  STEAM-BOILERS. 


421 


ment  of  the  various  accessory  members;  the  valves,  cocks,' and 
gauges,  if  attached  ;  and  every  detail,  great  or  small,  comparing 
all  with  the  specifications  and  drawings,  and  noting  any  defect, 
either  in  general  construction  or  in  workmanship.  Any  defec- 
tive material  or  bad  work  is  condemned,  and  must  be  replaced 


FIG.  ii2.— DEFECTIVE  PINNING. 


by  good  material  and  with  better  workmanship.     The  final  in- 
spection ^proving  satisfactory,  the  boiler  is  tested. 

The  defects  sometimes  revealed  by  inspection  are  flaws  in 
the  iron  in  parts  not  readily  seen  ;  inferior  iron  in  concealed 
portions  of  the  boiler  ;  cracked  flanges  or  laps,  either  in  lines 


422 


THE   STEAM-BOILER. 


from  rivet-hole  to  rivet-hole,  or  from  the  rivet  to  the  edge  of  the 
plate;  "unfair"  or  "half-blind  "  rivet-holes;  weak  and  narrow 


FIG.  113.— CORRECT  CONSTRUCTION. 

laps ;    injury  by  calking  or  by  chipping ;  laps  not  well  closed  ; 

narrow  water-spaces;    injured  tube-ends;  loose  and  badly  set 

and  fitted  braces  and 
pins  ;  omitted  stays  or 
braces  ;  and  minor  de- 
fects. 

To  ascertain  whether 
a  sheet  is  of  the  right 
thickness,  a  small  hole 
is  sometimes  drilled  at 
the  suspected  point. 
The  connecting  of 
stays  should  be  con- 


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FIG.  115. 


FIG.  116. 


demned  if 
Fig.  113; 
sometimes 


not  as  in 
they  are 
found  as 


dangerous  as  the  case  illustrated  in  Fig.  112. 

The  junctions  of  plates  meeting  at  the  intersections  of  seams 
are  given  the  shape  seen  in  the  accompanying  figures,  the  first 
showing  the  junction  ot  three  sheets  as  where  the  longitudinal 


CONSTRUCTION  OF  STEAM-BOILERS.  423 

and  transverse  seams  meet  in  overlapping  courses,  the  middle 
plate  being  thinned  to  give  proper  bearing. 

196.  Testing   Boilers,  when  under  inspection,  at  the  time 
of  acceptance,  usually  consists  simply  in  filling  them  with  cold 
water,  applying  a  pump,  and  subjecting  them  to  a  pressure  ex- 
ceeding that  at  which  they  are  to  be  used.     It  is  better  to  warm 
the  water  to    the   boiling-point  nearly,  as  the    pressure  then 
affects  a  boiler  more  nearly  as  under  the   conditions  of  actual 
use.     The    temperature    should   not   exceed  the  boiling-point 
under  atmospheric  pressure,  as  an  explosion  or  serious  rupture 
might  follow  the  revelation  of   a    defect — a  result  which  has 
actually  occurred  in  more  than  one  instance. 

The  pressure  should  be  applied  very  carefully  and  steadily, 
and  the  steam-gauge  watched  to  detect  any  sudden  drop  of 
pressure  which  would  indicate  yielding.  The  breaking  of  a 
brace  is  usually  revealed  by  a  sharp  report.  Gradual  yielding 
is  shown  by  a  cessation  of  rise  of  pressure,  or  by  its  falling  off. 
Leaks  show  themselves  whenever  seams  have  not  been  made 
tight,  and  are  traced  out  by  trickling  drops  or  running  streams, 
and  are  marked  with  chalk  or  a  pencil  for  later  calking.  The 
connection  of  large  steam-drums  or  domes  with  the  shell  are 
apt  to  show  weakness,  and  should  be  carefully  watched  as  pres- 
sure rises. 

The  pressure  is  finally  relieved,  the  boiler  emptied,  all  leaks 
stopped,  and  the  test  repeated  if  the  result  is  not  satisfactory. 
In  filling  boilers,  care  should  be  taken  to  run  them  full  of 
water  to  the  very  top  of  the  safety-valve  case ;  as  any  con- 
fined air  might  make  trouble. 

Testing  a  boiler  by  filling  it  to  the  safety-valve  with  cold 
water  and  then  starting  a  fire  is  advised  by  some  writers  as  a 
very  safe  method  ;  since  the  pressure  can  be  run  up,  if  the 
boiler  is  tight,  to  any  desired  point  without  exceeding  the  boil- 
ing-point under  atmospheric  pressure,  and  thus  without  danger 
in  case  of  a  weak  spot  revealing  itself.  The  temperature  should 
not  be  allowed  to.go  higher  than  that  limit,  as  a  boiler  filled 
with  water  at  the  temperature  due  a  high  steam-pressure  is 
more  dangerous  than  when  under  steam  at  the  same  pressure. 

197.  Sectional  Boilers  are  constructed,  so  far  as  composed 


424  THE   STEAM-BOILER. 

of  riveted  work,  precisely  as  are  other  boilers ;  but  they  are 
usually  constructed  mainly  of  nests  of  tubes,  connected  by  cast 
or  forged  "  headers,"  which  are  fitted  together  with  machined 
or  "  faced  "  joints,  and  held  by  bolts.  Each  header  has  its 
tube-end  either  screwed  or  expanded  into  it,  or  in  some  cases 
simply  slipped  into  place  and  made  tight  by  packing.  In  these 
boilers  the  special  precautions  to  be  observed  are  to  see  that 
the  joints  are  well  made  and  permanently  tight.  The  facing 
off  should  be  so  perfectly  done  that  a  thin  coat  of  red-lead 
paint,  at  most,  should  be  all  that  is  necessary  to  make  the 
joints  tight  against  any  steam-pressure.  The  best  makers 
do  not  even  use  this  precaution. 

198.  Transportation  and  Delivery  are  effected  usually  by 
the  maker.  Small  boilers  are  simply  loaded  on  strong  wagons 
and  carted  off  to  the  place  at  which  they  are  to  be  delivered. 
Heavier  boilers  often  require  specially  constructed  vehicles, 
and  the  very  cumbersome  structures  often  seen  where  marine 
flue-boilers  are  employed  are  sometimes  transported  on  skids 
and  rolls  as  houses  are  moved. 

In  hoisting  boilers  to  place  them  on  the  vehicles  on  which 
they  are  to  be  transported,  or  in  setting  them,  great  care  is  re- 
quired to  see  that  they  are  so  handled  as  to  introduce  no 
risk  of  straining  them.  The  best  method  of  slinging  them 
should  be  carefully  studied ;  the  tackles  used  should  be  of 
more  than  ample  strength,  and  no  risk  of  sudden  fall  or  change 
of  position  should  be  taken. 


CHAPTER  XL 

SPECIFICATIONS   AND   CONTRACTS. 

199.  The  Purpose  of  Specification  and  Contract  is  to 

present  a  perfectly  definite  and  exact  statement  of  the  charac- 
ter and  extent  of  the  work  to  be  done  :  the  forms  and  propor- 
tions of  details,  the  time  to  be  allowed  in  construction,  and  the 
amount  and  method  of  payments  to  be  made  by  the  purchaser. 
These  documents  are  always  prepared  when  any  work  of  im- 
portance is  to  be  done,  and  are  signed  by  the  two  contracting 
parties,  or  by  authorized  representatives  or  agents.  They  con- 
sist of  a  formal  contract,  or  statement  of  obligation,  with  spe- 
cifications describing  all  work  to  be  done,  and,  where  the  case 
permits,  of  a  set  of  drawings  of  everything  to  be  made,  in  full 
and  in  detail  ;  which  drawings  form  a  part  of  the  contract  as 
well  as  of  the  specification. 

200.  The  Contract  is  an  agreement  in  writing  by  which 
the  one  party  to  the   bargain  agrees  to  do  a  certain  exactly 
specified  work,  and  the  other  to  make  compensation  in  a  cer- 
tain stated  manner,  and  often  with  provision  of  penalties  for 
failure  to  fulfil  the  terms  of  the  contract.     This  agreement  rep- 
resents as  exactly  and  clearly  as   possible   the  mutual  under- 
standing between  the  contracting  parties  in  regard  to  all  busi- 
ness relations  involved  in  the  performance  of  the  work  to  be 
done.     Everything  needed  to  make  the  understanding  definite 
is  embodied  in   the  contract.     Advertisements,  proposals,  and 
preliminary  agreements  are  often  taken  as  parts  of  the  contract, 
as  well  as  drawings  and  specifications.     These  papers  are  made 
out  in  duplicate,  and  are  signed  by  both  sides,  each  retaining  a 
copy.     Where  many  interests  are  involved,  representatives  of 
each  should  sign  and  each  should  retain  a  copy. 

The  essential  conditions  of  a  legal  contract  are  that  it  shall 
be  definite  as  to  the  obligations  of  both  sides  ;  that  the  com- 


426  THE   STEAM-BOILER. 

pensation  be  stated  and  valid  ;  that  mutual  consent  be  secured 
by  voluntary  act ;  and  that  the  parties  in  interest  shall  all  sign 
of  their  own  free  will,  and  with  a  full  understanding  of  the  ob- 
ligation assumed.  The  mentally  or  legally  incompetent  cannot 
take  part  in  any  contract  while  such  disability  exists.  The 
agreement  is  interpreted  by  its  own  reading,  and  the  private 
intentions  of  the  makers  have  no  weight,  nor  have  their  mental 
reservations.  The  document  is  its  own  commentary  and  proof. 
Interpretations  of  terms  are  settled  by  the  customary  and  habit- 
ual use  of  the  term,  and  if  technical,  the  word  or  phrase  must 
be  taken  as  having  the  meaning  usual  in  the  business.  Obscur- 
ity of  wording  may  vitiate  the  agreement. 

The  duty  of  each  party  to  the  contract  is  to  be  separately 
defined  and  described.  The  contractor  is  bound  to  perform  a 
specified  work  in  a  satisfactory  manner,  to  complete  it  in  a  speci- 
fied time,  and  to  accept  a  stated  compensation,  made  in  a  man- 
ner and  as  to  time  clearly  prescribed.  The  other  party  to  the 
bargain  is  bound  to  make  full  compensation  to  the  extent  and 
in  a  manner  stated,  to  aid  in  all  proper  ways  in  the  carrying  of 
the  agreement  into  effect,  and  to  at  all  times  meet  the  con- 
tractor in  a  fair  and  helpful  spirit.  The  work  is  the  contractor's 
until  paid  for  as  prescribed  by  contract  ;  when  so  paid  for,  it 
becomes  the  property  of  the  employer,  who  only  then  carries 
any  risks  on  it,  unless  otherwise  provided  in  the  agreement. 

Penalties  incurred  by  non-fulfilment  of  the  terms  of  the  con- 
tract are  of  the  nature  of  a  standing  debt,  and  may  be  similarly 
held  and  collected.  Non-fulfilment  of  an  agreement  by  the  one 
side  does  not  necessarily  give  freedom  from  obligation  to  the 
other,  except  where  such  failure  on  the  one  side  may  interfere 
positively  with  the  operations  of  the  other.  In  statements  of 
time,  a  day  ends  at  midnight.  No  time  being  stated,  the  work 
mast  be  done  within  what  may  be  decided  to  be  a  "  reasona- 
ble" period. 

Action  at  law  must  usually  be  entered  against  one  guilty  of 
breach  of  contract  within  six  years ;  but  the  Statute  of  Limita- 
tions varies  in  different  states.  A  guaranty  and  bond  is  some- 
times exacted  to  insure  the  completion  of  the  contract ;  but 
this  is  usual  only  in  public  work. 


SPECIFICATIONS  AND    CONTRACTS.  427 

201.  The  Form  of  Specification  is  such  that  every  descrip- 
tive portion  of  the  contract  may  be  embodied   in  it,  in  a  sys- 
tematic manner,  in   proper  relative  order,  and   in   thoroughly 
definite  shape.     The  character  of  materials   to  be  employed  ; 
the  method  of  working  them  ;  their  final  form  ;  the  quality  of 
the  workmanship  ;  all  instructions  that  may  be  needed  in  regard 
to  the  performance  of  the  work — are  given  in  the  specifications. 
Since  this  document  is  that  on  which  the  intending  contractor 
makes   his   offer,    it    must    be    absolutely   complete,    and    as 
concise  as  possible.     No  detail  should  be  omitted,  and  nothing 
should  be  left  to  be  assumed  or  disputed. 

202.  Specifications  for  Steam-boilers  should  not  only  com- 
ply with  all  the  legal  conditions  of  a  sound  contract,  but  should 
represent  the  best   known  practice  of  the  time.     They  should 
be  prepared  by  the  designing  engineer,  and,  with  all  drawings, 
advertisements,  blank  proposals,  agreements,  and  intended  form 
of  contract,  laid  before  the  employer  for  careful  discussion  and 
final  approval  before  any  step  is  taken  in  the  receiving  of  bids 
or  the  acceptance  of  proposals.     They  should  include  a  full  de- 
scription of  the  boiler  to  be  built,  with  complete  drawings,  gen- 
eral and  in  detail ;  statements  of  the  kind,  make,  and  quality  of 
the  iron  or  steel  to  be  used,  the  character  of  the  workmanship 
to  be  demanded,  the  kind  of  tests  to  be  applied,  and  every  con- 
dition having  a  bearing  on  the  subject. 

203.  Sample  Specifications  are  as  follows,  illustrating  stan- 
dard practice  in  common  forms  of  boiler-work.     The   first*  is 
that  of  the  tubular  boiler  already  illustrated  in  §  15. 

SPECIFICATION  FOR  A  HORIZONTAL  TUBULAR  STEAM-BOILER. 

Type. — Boiler  to  be  of  the  horizontal  tubular  type,  with  overhanging 
front  and  doors  complete. 

Dimensions. — Boiler  to  be  16  feet  3  inches  long  outside,  and  60  inches 
in  diameter.  Tube-heads  to  be  15  feet  apart  outside. 

Steam-dome  to  be  33  inches  in  diameter  and  33  inches  high. 

Tubes — How  Set  and  Fastened. — Boiler  to  contain  66  best  lap- 

welded  tubes,  3  inches  in  diameter  by  15  feet  long,  set  in  vertical  and 

*  See  Am.  Engineer,  Nov.  1883:  Specifications  by  the  Hartford  Inspection 
and  Insurance  Co. 


*428  THE    STEAM-BOILER. 

horizontal  rows,  with  a  space  between  them,  vertically  and  horizontally, 
of  not  less  than  one  inch  (i"),  except  the  central  vertical  space,  which  is 
to  be  two  inches  (2"),  as  shown  in  drawing.  Tubes  to  be  set  sufficiently 
high  from  bottom  of  boiler  to  give  room  for  man-hole  and  access  to 
boiler  underneath  tubes,  as  shown  in  drawing.  No  tube  to  be  nearer 
than  3  inches  to  shell  of  boiler.  Holes  through  heads  to  be  neatly 
chamfered  off.  All  tubes  to  be  set  by  a  Dudgeon  expander,  and  slightly 
flared  at  the  front  end,  but  turned  over  or  beaded  down  at  back  end. 


FOR   IRON   PLATES. 

Quality  and  Thickness  of  Iron  Plates. — Shell  plates  to  be  of  an 

inch  thick,  of  the  best  C.  H.  No.  i  iron,  with  brand,  tensile  strength,  and 
name  of  maker  plainly  stamped  on  each  plate.  Tensile  strength  to  be  not 
less  than  50,000  pounds  per  square  inch  of  section,  with  a  good  per- 
centage of  ductility.  Heads  to  be  of  an  inch  thick,  *of  the  best 
C.  H.  No.  i  flange-iron. 

FOR   STEEL. 

Steel  Plates. — Shell-plates  to  be  of  an  inch  thick,  of  homogene- 

ous steel  of  uniform  quality,  having  a  tensile  strength  of  not  less  than 
60,000  pounds  per  square  inch  of  section,  nor  more  than  65,000  pounds 
with  45  per  cent  ductility,  as  indicated  by  the  contraction  of  area  at 
point  of  fracture  under  test.  Name  of  maker,  brand,  and  tensile  strength 
to  be  plainly  stamped  on  each  plate.  Heads  to  be  of  same  quality  as 
plates  of  shell  in  all  particulars,  of  an  inch  thick. 

Flanges. — All  flanges  to  be  turned  in  a  neat  manner  to  an  internal  ra- 
dius of  not  less  than  two  inches  (2"),  and  to  be  clear  of  cracks,  checks,  or 
flaws. 

Riveting. — Boiler  to  be  riveted  with  f-inch  rivets  throughout.  All 
girth  seams  to  be  single-riveted.  All  horizontal  seams  and  flange  of 
dome  at  junction  of  shell  of  boiler  to  be  double  staggered  riveted.  Rivet- 
holes  to  be  punched  or  drilled  so  as  to  come  fair  in  construction.  No 
drift-pin  to  be  used  in  construction  of  boiler.  A  reamer  to  be  used  in  all 
cases  to  bring  the  holes  "  fair." 

Braces. — There  are  to  be  twenty-two  (22)  braces  in  boiler — seven 

(7)  on  each  head  above  the  tubes,  and  six  (6)  on  rear  head  and  two  (2) 
on  front  head  below  the  tubes,  as  shown  in  drawing,  none  of  which  are 
to  be  less  than  three  (3)  feet  long.     Braces  to  be  made  of  best  round 
iron,  of  one  (i)  inch  in  diameter,  and  of  single  lengths. 

How  Set  and  Fastened. — There  are  to  be  five  (5)  lengths  of  T-iron, 
four  (4)  inches  broad  and  one  half  (-J-)  inch  thick,  Three  (3)  being  eight 

(8)  inches  long,  Two  (2)  being  fourteen  (14)  inches  long,  placed  radially, 
and  riveted  with  f-inch  rivets  to  each  head  above  the  tubes,  as  shown 


SPECIFICATIONS   AND    CONTRACTS,  429 

in  drawing.  There  are  to  be  four  (4)  lengths  of  T-iron,  four  (4) 
inches  broad  and  one  half  (J)  inch  thick,  two  (2)  being  six  (6)  inches 
long  and  two  (2)  being  twelve  (12)  inches  long,  placed  radially,  and  riv- 
eted on  rear  head  below  the  tubes,  also  two  (2)  lengths,  six  (6)  inches 
long,  riveted  on  front  head  below  the  tubes,  each  side  of  man-hole,  as 
shown  in  drawing.  The  holes  for  fastening  the  braces  to  these  radial 
brace-bars  are  all  to  be  drilled.  The  braces  are  to  be  fastened  with  suit- 
able jaws  and  turned  pins  or  bolts,  so  as  to  realize  strength  equal  to  inch- 
round  iron.  Braces  to  be  set  as  shown  in  drawing,  and  to  bear  uniform 
tension,  and  to  be  fastened  on  shell  of  boiler  with  two  (2)  f-inch  rivets 
each. 

Dome. — Dome  to  be  constructed  of  same  quality  of  iron  or  steel  as 
heads  of  boiler,  of  an  inch  thick,  and  head  to  be  of  same  quality  of 

iron  or  steel  as  heads  of  boiler,  of  an  inch  thick.  Dome-head  to  be 

braced  with  six  (6)  f-inch  braces,  reaching  from  head  well  down  on 
shell,  as  shown  in  drawing,  and  fastened  at  each  head  with  two  (2)  f- 
inch  rivets.  Opening  from  boiler  into  dome  to  be  inches  in  diam- 

eter. There  are  to  be  two  pieces  of  T-iron  riveted  on  to  outside  of  boiler 
shell,  within  the  dome  girthwise,  one  on  each  side  of  opening,  as  shown 
in  drawing;  also  suitable  drip  holes  to  be  cut  at  junction  of  shell  and 
dome. 

Man-holes. — .Boiler  to  have  two  man-holes,  each  eleven  (11) 

inches  by  fifteen  (15)  inches,  with  strong  internal  frames  (as  shown  in 
drawing),  and  suitable  plates,  yokes,  and  bolts,  the  proportions  of  the 
whole  such  as  will  make  them  as  strong  as  any  other  section  of  the  shell 
of  like  area.  One  to  be  placed  in  front  head  underneath  the  tubes,  and 
one  to  be  placed  on  shell  of  boiler,  as  shown  in  drawing. 

Hand-holes. — Boiler  to  have  one  hand-hole,  with  suitabLs  plate, 

yoke,  and  bolt,  located  in  rear  head  below  the  tubes,  as  shown  in  the 
drawing. 

Nozzles. — Boiler  to  have  two  cast-iron  nozzles,  four  (4)  inches  in- 

ternal diameter,  one  for  steam  and  the  other  for  safety-valve  connections, 
securely  riveted  to  head  of  dome,  as  shown  in  drawing. 

Wall-plates. — Boiler  to  have  four  cast  lugs,  two  on  each  side, 

securely  riveted  in  place,  each  twelve  (12)  inches  long,  with  a  projection 
of  nine  (9)  inches  from  the  boiler,  the  rear  lugs  each  to  rest  on  three 
transverse  rollers,  one  inch  in  diameter,  which  are  to  rest  on  suitable 
cast-iron  wall-plates,  as  shown  in  drawing,  front  lugs  to  rest  on  suitable 
wall-plates,  without  rollers. 

Blow-out. — For  blow-out  connection,  one  plate,  one  half  inch  thick,  to 
be  secured  with  rivets  driven  flush  on  inside  of  the  shell,  and  tapped  to 
receive  a  two  (2)  inch  blow-pipe. 

Front. — Boiler  to  be  provided  with  cast-iron  front  and  all  the 

requisite  doors  and  fastenings  for  facility  of  access  to  tubes,  furnace,  and 


430  THE   STEAM-BOILER. 

ash-pit.  All  to  be  of  substantial  construction,  neat  appearance,  and 
close-fitting. 

Buckstaves — Grate-bars. — Boiler  to     be     provided    with 

buckstaves ;  also  all  bolts,  rods,  nuts,  and  washers,  anchor-bolts  to  ex- 
tend  in  setting  beyond  bridge-wall ;  also  bearer  and  grate  bars  (pattern 
to  be  selected);  also  cast-iron  door,  to  be  at  least  two  (2)  feet  by  three 
(3)  feet  and  provided  with  liner  plate,  for  back  tube-door— and 
door  fifteen  inches  by  fifteen  inches  for  flue  for  side  or  rear  end. 

Fittings. — Boiler  to  be  provided  with  one  safety-valve, 

inches  in  diameter,  one  inch  steam-gauge  of  standard  make,  three 

gauge-cocks  properly  located,  also  one  glass  water-gauge,  a  two-inch 
open-way  blow-valve,  and  feed  and  check  valves,  each  one  and  one 
quarter  inch.  Feed  to  be  introduced  into  front  head  of  boiler,  above 
tubes.  Feed-pipe  to  extend  well  back  towards  rear  of  boiler,  across 
tubes,  and  turn  down  between  tubes  and  shell,  as  shown  in  drawing. 

Fusible  Plug. — Boiler  to  be  provided  with  a  fusible    plug  so 

located  that  its  centre  shall  be  two  inches  above  upper  row  of  tubes  at 
back  end. 

Damper. — Boiler  to  be  provided  with  a  damper  with  suitable 

hand  attachments,  easily  accessible  at  the  front  of  the  boiler,  damper  to 
be  fitted  to  the  throat  of  the  smoke-arch,  as  near  as  practicable  to  the 
tube-openings,  and  of  area  equal  to  the  cross-section  of  all  the  tubes. 

The  size  and  description  of  parts  to  conform  substantially  to  the  de- 
tails of  the  accompanying  plan.     All  the  above  to  be  delivered  at 

and  all  the  material  and  workmanship  to  be  subjected  to  inspection  and 
approval. 

The  following  are  specifications  for  a  marine  flue-boiler  for 


SPECIFICATION  FOR  FLUE-BOILER. 

There  is  to  be  one  boiler  of  the  flue  and  return-tube  type,  of  the  fol- 
lowing general  dimensions : 

Extreme  length 13  feet. 

Diameter  of  shell 8     " 

Width  of  front 8     " 

Diameter  of  steam-chimney 5     " 

Diameter  of  steam-chimney  lining 3     " 

Height  of  steam-chimney  above  shell 5     " 

*  For  very  elaborate  and  complete  naval  specifications,  see  Shock's  '"Treat- 
ise on  Steam  Boilers."     New  York:  D.  Van  Nostrand. 


PECIFICATIONS  AND    CONTRACTS.  431 

There  are  to  be  two  furnaces,  each  forty  two  inches  wide  and  six  feet 
long.  Bottom  of  furnace-legs  to  drop  six  inches  below  shell.  Bridge-wall 
seven  inches  thick.  Combustion-chamber  of  back  furnaces  in  one  twenty- 
four  inches  deep.  Back  connection  twenty-eight  inches  deep.  Front 
connection  twenty-eight  inches  deep.  Furnace-crowns  to  be  a  semi- 
circle. To  have  two  16  inch,  two  12-inch,  two  ii-inch,  and  four  p-inch 
direct  flues,  all  fifteen  inches  long,  and  ninety  return  tubes,  seven  feet 
ten  inches  long. 

All  the  horizontal  shell-seams  to  be  double  riveted,  also  the  bottom 
course  of  steam-chimney  where  riveted  to  shell  and  vertical  seams. 
Back  part  of  furnace,  where  connected  to  shell,  to  be  double-riveted  one 
third  distance  around,  the  remainder  of  riveting  about  the  boiler  to  be 
single. 

Thickness  of  Plates. — To  be  as  follows  :  tube-sheets  ^,  shell  of  boiler 
(round  part)  f,  bottom  course  of  steam-chimney  -fa,  inside  lining  of  steam- 
chimney  -f,  the  balance  of  the  iron  in  the  boiler  to  be  T5-^,  except  bottoms 
of  furnace  legs,  which  are  to  be  f. 

Material. — Furnaces  to  be  of  steel,  and  the  balance  of  the  iron  in  the 
boiler  to  be  of  the  best  C.  H.  No.  i,  and  flange  iron,  and  all  stamped 
50,000  pounds  T.  S.  All  flat  surfaces  to  be  braced'  6^-inch  centres,  with 
hot  sockets  wherever  practicable. 

Boiler  to  be  fitted  with  man-hole  in  top  of  shell,  also  in  front  in  the 
spandrels  over  furnace  crowns.  Openings  to  be  surrounded  by  a  wrought- 
iron  ring  i\  inches  wide  by  f  inch  thick,  riveted  to  shell.  Hand-holes  to 
be  cut  in  legs  and  every  part  where  necessary  to  facilitate  cleaning.  Man 
and  hand  holes  to  be  furnished  with  plates  and  bolts  complete. 

Front  connection  to  be  fitted  with  wrought- iron  doors,  fitted  with 
wrought-iron  linings,  and  fitted  with  two  registers.  Furnace-doors  to 
be  of  wrought-iron  with  cast-iron  perforated  linings,  to  be  fitted  with 
wrought-iron  hinges,  latches,  etc.,  complete.  A  suitable  opening  with 
door  to  be  provided  in  back  connection. 

Grates  and  Bearers. — Boiler  to  set  on  three  cast-iron  legs  under  fur- 
naces running  the  whole  length,  about  12  inches  high,  and  fitted  with 
supports  for  grate-bar  bearers.  Grates  to  be  6  feet  long  in  two  lengths. 
Ash-pans  of  cast-iron  to  be  laid  in  brick  and  cement.  Back  ends  of  legs 
to  be  closed  in  with  No.  10  sheet-iron. 

Shell  of  boiler  to  rest  on  a  cast-iron  saddle  in  two  halves  firmly 
bolted. 

Test. — The  boiler  before  being  hoisted  into  the  vessel  is  to  be  sub- 
jected to  a  hydrostatic  pressure  of  100  pounds  per  square  inch. 

Boiler  Connections. — Smoke-pipe  36  inches  diameter,  and  to  extend 
16  feet  above  top  of  steam-chimney,  to  be  made  of  No.  12  iron,  to  be 
finished  with  angle-iron  top,  bead-iron  joints,  six  chain-stays  and  damper, 
.arranged  to  be  operated  from  the  fire-room.  Lower  part  of  smoke-pipe 


432  THE   STEAM-BOILER. 

to  be  bolted  to  the  steam-chimney,  the  inside  lining  being  carried  up  for 
this  purpose.  Chain-stays  to  be  provided  with  turn  buckles  to  take  up 
the  slack. 

Steam-chimney  to  be  encased  with  No.  16  sheet-iron  and  fitted  with  a 
stopping-cap  in  two  halves.  A  chamber  of  cast-iron  is  to  be  bolted  to 
the  steam-chimney,  containing  the  safety-valve  and  stop  valve,  each  to 
be  five  inches  in  diameter,  with  top  of  trumpet  shape.  Surface  and 
bottom  blows  to  be  provided  with  screw  stop-valve  for  the  former  and 
cock  for  the  latter,  secured  on  the  boiler.  Blows  to  be  led  out  of  the 
vessel  below  the  water-line  through  a  suitable  valve. 

There  is  to  be  a  feed-valve  on  each  side  of  boiler  in  front,  in  con- 
nection with  check-valve,  one  to  be  for  the  donkey  and  the  other  for  the 
main  feed-pumps,  both  to  be  of  composition  and  2  inches  diameter. 
Gauge-cocks  and  glass  water-gauge  to  be  placed  on  a  stand-pipe,  con- 
nected to  the  boiler.  Boiler  to  be  covered  with  i^-inch  felt,  canvased 
and  painted,  felt  to  be  secured  with  necessary  bands  around  steam-chim- 
ney. 

Steam  Pump. — To  be  an  approved  steam-pump  with  2^-inch  water- 
plunger,  and  fitted  with  hand-gear.  To  be  connected  with  necessary 
receiving-pipes  from  bilge  and  sea  cock,  and  delivery-pipes  to  boiler,  over- 
board and  for  fire  hose,  each  branch  to  be  fitted  with  a  proper  screw- 
valve.  Exhaust-pipe  to  lead  overboard,  awash  with  water-line ;  all  the 
donkey  pump-pipes  to  be  of  wrought-iron,  galvanized. 

The  following  is  a  general  proposal-specification  for  "  sec- 
tional boilers,"  purposely  left  somewhat  elastic  to  admit  all 
bidders :  * 

SECTIONAL  STEAM  BOILERS. 

Boiiers. — Proposals  will  be  received  for  two  (2)  sectional  or  water- 
tube  steam-boilers  of  nine  hundred  (900)  superficial  feet  of  heating-sur- 
face each,  or  eighteen  hundred  (1800)  superficial  feet  of  heating  in  the 
aggregate  for  both  boilers. 

Details. — The  proposals  must  be  for  the  two  (2)  steam-boilers  complete 
with  cast-iron  fronts,  grate  bars  and  bearers,  ash-pit  and  side  doors  and 
frames,  steam  and  water  gauges,  check  and  blow-off  valves,  safety-valves 
of  the  pop  pattern,  smoke  connection  for  chimney,  damper  and  rods,  and 
a  steam  main  connected  with  the  steam  drums  of  the  two  boilers,  together 
with  all  bolts,  beam-columns  and  materials  necessary  for  the  proper 
erection  of  said  boilers  upon  the  grounds  of  the  gas  company  in  the  city 
of  Cincinnati. 


*  Issued  by  the  Cincinnati  Gas  Co.,  as  prepared  by  Mr.  J.  W.  Hill,  1883. 


SPECIFICATIONS  AND    CONTRACTS.  433 

Erection. — The  proposals  must  embrace  the  construction,  erection,  and 
trimming  of  said  boilers  complete,  excepting  connection  of  steam-main 
with  company's  steam-pipe.  The  contractors  to  turn  over  the  plants  to 
the  company  ready  for  use. 

Tubes. — The  tubes  in  the  boilers  shall  be  lap-welded,  of  three  and 
one  half  (3.5)  inches,  or  four  (4)  inches,  external  diameter  (at  the  option 
of  the  contractor),  of  such  length  and  arrangement  in  connection  with 
steam  and  water  drums  as  may  seem  proper  to  the  contractor. 

Steam  Drums. — The  steam-drums  shall  be  twenty-eight  (28)  inches 
diameter,  of  Otis  or  equivalent  soft  steel  plates,  of  a  tensile  strength  of 
seventy  thousand  (70,000)  pounds  per  square  inch  of  section,  of  three- 
eighths  (-375)  inch  thickness,  with  double-riveted  longitudinal  seams, 
and  furnished  with  heads  corresponding  in  quality  and  strength  with  the 
steel  shell. 

Steam  Mains. — The  steam- mains  shall  be  eighteen  (18)  inches  diam- 
eter, of  Otis  or  equivalent  steel  plates,  of  a  tensile  strength  of  seventy 
thousand  (70,000)  pounds  per  square  inch  of  section,  of  one  quarter  (.25) 
inch  thickness,  with  double-riveted  longitudinal  seams,  and  with  heads 
corresponding  in  quality  and  strength  with  the  steel  shell. 

Water  Drums. — The  water-drums  may  be  of  cast-iron  or  wrought- 
iron,  at  the  option  of  the  contractor,  of  sixteen  (16)  inches  diameter,  and 
shall  be  of  same  relative  strength  as  the  steam-drums. 

Sample  Joint. — Each  proposal  shall  be  accompanied  by  a  sample 
joint,  such  as  will  be  used  in  connecting  the  tubes  to  the  headers,  or  to 
the  steam  and  water  pumps ;  and  shall  contain  a  detailed  schedule  (writ- 
ten or  printed)  of  all  the  material  dimensions  of  parts  subject  to  strain, 
(pressure)  and  shall  be  accompanied  by  a  scale-drawing  [one  and  one 
half  (1.5)  inches  to  the  foot]  of  front  elevation,  transverse  and  longi- 
tudinal sections,  and  plan  of  boilers  set  in  brick-work  ready  for  smoke 
connections  with  chimney. 

Chimney. — The  company  will  furnish  a  brick  chimney,  properly 
located,  octagonal  in  form,  of  an  internal  cross-section  of  twelve  (12) 
superficial  feet,  increasing  gradually  in  internal  diameter  from  bottom  to- 
top,  and  ninety  (90)  feet  six  (6)  inches  high  from  level  of  boiler-house 
floor. 

Heating  Surface. — The  proposals  must  state  exact  heating-surface,, 
measured  upon  inner  diameter  of  tubes,  and  outer  diameter  of  steam- 
drums  (or  steam  and  water  drums). 

Grate  Surface. — Grate-surface  and  area  of  cross-section  of  smallest 
throat  through  which  the  hot  gases  must  pass  to  chimney,  and  area  of 
cross-section  of  smoke  connection  with  chimney  to  be  stated. 

Smoke  Holes. — (The  openings  one  upon  either  side  of  stack  to  receive 
the  smoke  connections  will  have  an  area  of  six  (6)  superficial  feet  each, 
and  will  be  two  (2)  feet  wide  horizontal  diameter,  and  three  and  forty- 
28 


434  THE   STEAM-BOILER. 

three  hundredths  (3.43)  feet  long  vertical  diameter,  with  semicircular  ends 
struck  upon  a  radius  of  one  (i)  foot.) 

Fuel. — The  fuel  to  be  fired  under  the  boilers  will  be  "  Breeze"  or  coke 
screenings,  a  smokeless  fuel  containing  from  twelve  (12)  to  fifteen  (15) 
per  cent  of  non-combustible  matter. 

Guarantees. — Each  proposal  must  contain  a  guarantee  of  capacity  of 
not  less  than  four  (4)  pounds  of  steam  per  hour  per  superficial  foot  of 
heating-surface,  with  moderate  firing;  and  shall  contain  a  guarantee  of 
economy  of  not  less  than  eight  (8)  pounds  of  steam  exclusive  of  water  (if 
any)  entrained  from  and  at  212°  Fahr.  per  pound  of  "  Breeze." 

Test  Trial. — When  the  boilers  are  erected  and  completed,  a  test-trial 
for  capacity  and  economy  shall  be  made  by  the  contractor,  under  direc- 
tion of  the  company. 

Failure  to  Comply. — Should  the  boilers  fail  to  comply  with  the  con- 
tractors' guarantees  for  economy  or  (and)  capacity,  or  in  any  other  respect, 
a  reasonable  time  not  in  excess  of  sixty  (60)  days  shall  be  given  the  con- 
tractor to  remedy  such  defects;  failing  in  which  the  boilers  and  all 
appurtenances  belonging  thereto  and  furnished  by  the  contractor  shall, 
at  the  option  of  the  company,  be  removed  within  thirty  (30)  days  from 
order  of  such  removal. 

Time. — The  proposal  must  name  the  time  after  acceptance  required 
for  completion  of  boilers  as  per  invitation. 

Terms  of  Payment. — One  half  of  the  contract  price  for  said  boilers 
will  be  paid  upon  completion,  and  after  the  test-trial  and  acceptance  as 
herein  provided  ;  and  the  balance  within  thirty  (30)  days  thereafter. 
The  company  reserves  the  right  to  reject  any  or  all  proposals  submitted. 

The  following  are  two  dimension-specifications  of  boilers 
and  locomotives  as  issued  by  the  Pennsylvania  Railway  Motive 
Power  Department : 


STANDARD  P.  R.  R.  CLASS  "  R"  FREIGHT  ENGINE  WITH  TENDER. 

Boiler  material, Steel. 

Thickness  of  boiler-sheets,  dome,  and  extended  smoke-box,           .  T5^  in. 

Thickness  of  boiler-sheets,  barrel,            T\  in. 

"                "              "        outside  fire-box,            .        .        .    •     .  f  in. 

"  "  "        smoke-box,  sheet  under  dome,  waist, 

and  throat, -^  in. 

Max.  internal  diameter  of  boiler,  /  Bdpaire  fire.box?                        \  6of  in. 

Min.  internal  diameter  of  boiler,  )                                                         (  59  in. 

Height  to  centre  of  boiler,  from  top  of  rail,            .        .         .        .  89  in. 

No.  of  tubes,               183. 


SPECIFICATIONS  AND    CONTRACTS.  435 

nside  diameter  of  tubes,  ........     2j  in. 

Outside       "  "  ........     2%  in. 

Tube  material,  ........      Wrought-iron. 

Length  of  tubes  between  tube-  sheets,       .....        156^!  in. 

External  heating-surface  of  tubes,  ....      1,564.24  sq.  ft. 

Fire-area  through  tubes,  .......         5  sq.  ft. 

Length  of  fire-box  at  bottom  (inside),      .....  107  in. 

Width  of  "  "  .....  42  in. 

Height  of  crown-sheet,  above  top  of  grate  (centre  of  fire-box),        51^  in. 
Inside  fire-box  material,  ........    Steel. 

Thickness  of  inside  fire-box  sheets,  sides,        .....      i  in. 

front,  back,  and  crown,  .     -^  in. 

Thickness  of  tube  sheets,  ........       -J-  in. 

Tube-sheet  material,          .........     Steel. 

Heating-surface  of  fire-box,       ......  166.8  sq.  ft. 

Total  heating-surface,        .....         .         .      1,731.04  sq.  ft. 

Fire-grate  area,  ........  31.1  sq.  ft. 

Max.  diameter  of  smoke-stack,  I   r     -     \  j  26f  in. 

Min.         "  f  (     18  in. 

STANDARD  P.  R.  R.  CLASS  "  P"  PASSENGER  ENGINE  WITH  TENDER. 

Boiler  material,            .         .         .         .....         .  Steel. 

Thickness  of  boiler-sheets,  dome  ......         .  T5-g-  in. 

"       barrel,  and  outside  fire-box,    .         .  f  in. 

Thickness  of  boiler-sheets,  slope,  roof,  waist,  and  smoke-box,  T7^  in. 

Max.  internal  diameter  of  boiler,  )  Wagon.top  {  5^1  in. 


Min.         "  "  (  53^  in. 

Height  to  centre  of  boiler  from  top  of  rail,         ....       86£  in. 

No.  of  tubes,  .  ........  240. 

Inside  diameter  of  tubes,     .         .        .         .....         if  in. 

Outside      "  "  ...         ......  2  in. 

Tube  material,  .......          Wrought-iron. 

Length  of  tubes  between  tube-sheets,        ....  I3OTV  in. 

External  heating  surface  of  tubes,  .         .         .  1,365.81  sq.  ft. 

Fire-area  through  tubes,      .......  4  sq.  ft. 

Length  of  fire-box  at  bottom  (inside)  .....        9  ft.  1  1|  in. 

Width          "       ••  "  «  ....          3  ft.  5f  in. 

Height  of  crown-sheet  above  top  of  grate,  centre  of  fire-box,    3  ft.  10  in. 
Inside  fire-box  material  .........        Steel. 

Thickness  of  inside  fire-box  sheets,  sides,  .         •        .         .          J  in. 

"        front,  back,  and  crown,          .        .        T5^-  in. 

Thickness  of  tube-sheets,  .......  ^  in. 

Tube-sheet  material,  Steel. 


43 6  THE   STEAM-BOILER. 

Heating-surface  of  fire-box, 164.39  scl-  ft. 

Total  heating- surface,          .......    1,530.2  sq.  ft. 

Fire-grate  area,  34.8  sq.  ft. 

Diameter  of  smoke-stack  (straight), 18  in. 

Height  of  stack  above  top  of  rail, 15  ft.  o  in. 

204.  Quality  of  Material  and  methods  of  test  are  often 
specified  very  minutely,  and  are  sometimes  settled  by  legal 
provisions.  Thus  the  British  "Admiralty"  issue  the  following 
requirements,  other  than  the  ordinary  tensile  tests,  for  test  of 
irons : 

Samples  of  B.  B.  iron  I  inch  (2.54  centimetres)  thick  are  to 
bend  cold,  without  fracture,  to  an  angle  of  15°  with  the  grain 
and  5°  across  the  grain;  -J  inch  (1.27  centimetres)  plates,  35° 
and  15°  respectively;  T3¥  inch  (0.48  centimetre)  and  under  must 
bend  90°  and  40°.  When  hot,  plates  I  inch  (2.54  centimetres) 
and  under  must  bend  125°  with  and  90°  across  the  grain. 

For  B.  iron,  the  requirements  are : 

THICKNESS.  ANGLE.  ANGLE. 

Inches.         Centimetres.  With  the  grain.  Across  the  grain, 

i  2.54  10°  5° 

I  1.27  30°  10° 

T\  0.48  and  under.  75°  30° 

Test-pieces  to  be  4  feet  (1.22  metres)  long  with  the  grain 
and  full  width  of  plate  across  the  grain. 

The  plate  should  be  bent  from  3  to  6  inches  (7.62  to  15.24 
centimetres)  from  the  edge. 

The  Admiralty  tests  for  steel  are  the  following  when  selecting 
mild-steel  ship-plates : 

Tenacity  from  26  to  30  tons  per  square  inch  (4100  to  4700 
kilogrammes  per  square  centimetre).  Extension  at  least  20 
per  cent  in  a  length  of  8  inches  (19.3  centimetres). 

Longitudinal  strips  planed  down,  I J  inches  (3.8  centimetres) 
wide,  heated  to  low  cherry-red,  cooled  in  water  82°  Fahr.  (28° 
Cent.),  must  bend,  in  the  press,  to  a  curve  of  radius  equal  to 
one  and  a  half  times  the  thickness. 

Plates  must  be  free  from  lamination  and  injurious  surface 
defects. 

One  plate  in  every  fifty  in  any  invoice  is  to  be  tested. 


SPECIFICATIONS  AND    CONTRACTS.  437 

Test-pieces  to  be  8  inches  (20.32  centimetres)  long,  or  more, 
and  parallel. 

Weight  is  estimated  at  forty  pounds  per  square  foot  for  one 
inch  thick,  with  a  variation  allowable  of  5  per  cent  (lighter 
weight  only)  on  plates  of  half  inch  thick  or  thicker. 

The  same  specifications  apply  to  bulb,  bar,  and  angle  steel. 

Lloyd's  rules  allow  for  one  ton  higher  tenacity  and  one  half 
the  bend  specified  by  the  Admiralty.  Masts  and  yards  are  to 
be  made  of  iron  having  a  tenacity  of  20  tons  per  square  inch, 
(3150  kilogrammes  per  square  centimetre). 

In  working,  all  plates  and  bars  are  to  be  bent  cold  when 
possible,  and  heating  only  resorted  to  when  unavoidable.  All 
parts  that  have  been  heated  must  be  annealed  as  a  whole,  if 
possible,  and  if  not,  a  little  at  a  time.  When  necessary,  long 
pieces  may  be  made  up  of  shorter  ones  with  butted  joints 
shifted  and  strapped  securely.  No  pieces  failing  in  the  working 
can  be  used,  but  samples  must  be  cut  from  them  and  forwarded 
to  the  Admiralty  for  examination.  Work  must  be  finished 
above  a  black  heat.  Hammering  is  objected  to,  and  the 
hydraulic  press  used  for  bending  when  practicable. 

An  American  railroad  makes  the  following  specifications  for 
materials  supplied  to  the  repair-shops : 

Specifications  for  Common  Bar  Iron. — Grain. — To  be  uni- 
form and  fibrous,  rather  than  granular  in  texture.  Workman- 
ship.— All  bars  to  be  smoothly  rolled  and  to  be  accurately 
gauged  to  size  ordered.  Tensile  Strength. — To  average  55?000 
pounds  per  square  inch  (3,867  kilogrammes  per  square  centi- 
metre), and  no  iron  to  be  received  less  than  50,000  pounds  to 
square  inch  (3,515  kilogrammes  per  square  centimetre).  Work- 
ing Test. — A  three-quarter-inch  bar  bent  double,  cold,  to  show 
no  fracture ;  the  same  bar,  heated,  to  be  bent  and  also  to  be 
drawn  to  a  point  showing  no  tendency  to  "  red-shortness." 

Specifications  for  Stay-bolt  Iron. — Grain. — To  be  uniform 
and  of  a  fibrous  nature.  Iron  to  be  soft  and  easily  worked. 
Tensile  Strength. — To  be  60,000  pounds  to  the  square  inch 
(4218  kilogrammes  per  square  centimetre).  Working  Test. — 
A  bar  three-quarter  inch  diameter  to  be  bent  cold,  showing  no 
flaw ;  a  piece  of  same  diameter,  having  thread  cut  on  it,  may 


43$  THE    STEAM-BOILER. 

show  opening  when  bent  double,  cold,  but  such  opening  should 
not  extend  more  than  one  eighth  of  an  inch  in  depth.  When 
put  into  the  boiler  the  metal  should  not  become  brittle 
when  hammered  down  to  form  a  head. 

205.  The  Duties  of  the  Inspector  are  such  as  demand  the 
utmost  care,  considerable  skill,  and  a  large  amount  of  experience, 
together  with  a  good  judgment  and  absolute  conscientiousness. 
He  must  also  be  a  man  of  sufficient  strength  of  character  to  do 
his  duty  by  his  employers,  whatever  influences  may  be  brought 
to  bear  upon  him  to  induce  him  to  pass  work  or  material  which 
does  not  fully  comply  with  the  specification.  He  is  expected 
to  examine  all  material  with  a  view  to  the  determination,  both 
of  its  full  compliance  with  the  terms  of  the  specification  and 
contract,  and  of  its  general  fitness  for  the  work. 

The  first  step  in  inspection  is  a  careful  measurement  of  the 
piece  offered  for  examination,  and  a  comparison  with  the  draw- 
ing, model,  pattern,  or  template,  to  ascertain  if  it  is  made 
exactly  to  size. 

Exact  workmanship  is  often  secured  by  a  system  of  standard 
gauges.  This  is  especially  the  case  where  machines  are  made 
in  large  numbers.  The  modern  method  of  manufacturing 
machinery  for  the  market  compels  the  adaptation  of  special 
tools  to  the  making  of  special  parts  of  the  machines,  and  the 
appropriation  of  a  certain  portion  of  the  establishment  to  the 
production  of  each  of  these  pieces,  while  the  assembling  of  the 
parts  to  make  the  complete  machine  takes  place  in  a  room  set 
apart  for  that  purpose.  But  this  plan  makes  it  necessary  that 
every  individual  piece  of  any  one  kind  shall  fit  every  individual 
piece  of  a  certain  other  kind  without  expenditure  of  time  and 
labor  in  adapting  each  to  the  other. 

This  requirement,  in  turn,  makes  it  necessary  that  every 
piece,  and  every  face  and  angle,  and  every  hole  and  every  pin 
in  every  piece,  shall  be  made  precisely  of  this  standard  size,' 
without  comparison  with  the  part  with  which  it  is  to  be  paired  ; 
and  this  last  condition  compels  the  construction  of  gauges 
giving  the  exact  size  to  which  the  workman  or  the  machine 
must  bring  each  dimension. 

Sizes    being    found    right,  the    quality  of   the    material    is 


SPECIFICATIONS  AND   CONTRACTS.  439 

determined  by  examination  and  test ;  defective  welds,  lamina- 
tion, and  cracks  are  found  and  condemned.  A  blow  with  a 
hammer  often  reveals  unsoundness,  and  a  laminated  plate  may 
be  detected  by  suspending  it  and  tapping  it  all  over.  If  the 
defect  appears  on  the  surface,  the  sheet  may  be  supported  by 
the  corners  in  the  horizontal  position,  and  water  poured  on  it 
at  the  line  indicating  lamination,  and  then  tapping  it  with  a 
hammer.  The  liquid  will  work  into  the  sheet,  lifting  the  surface 
lamina  and  revealing  the  extent  of  the  defect. 


CHAPTER  XII. 

THE   MANAGEMENT   AND    CARE    OF   BOILERS. 

206.  The  Management  of  Steam  Boilers,  it  may  be  stated 
generally,  demands  in  the  highest  degree  care,  conscientious- 
ness, and  unintermitted  vigilance.  The  value  of  the  property 
entrusted  to  the  attendants  is  so  great  and  the  consequences  of 
ignorance  or  neglect  in  operation  are  so  serious,  and  may  be  so 
disastrous,  that  no  possible  excuse  can  be  given  for  negli- 
gence on  the  part  of  the  proprietor  or  his  responsible  repre- 
sentative, in  securing  intelligent,  experienced,  and  trustworthy 
attendants,  or  on  the  part  of  the  attendants,  whether  engineer 
in  charge,  fireman  ("  stoker"),  or  water-tender,  in  the  manage- 
ment of  the  boiler. 

The  care  demanded,  in  ordinary  working,  to  keep  a  full  sup- 
ply of  water,  to  preserve  the  fires  in  their  most  effective  condi- 
tion, to  keep  an  even  steam-pressure,  an  ample  and  unintermit- 
tent  supply  of  steam,  is  such  as  tries  ^the  best  of  men  ;  but, 
added  to  this,  it  is  imperative  that  the  responsible  man  in  charge 
of  boilers  have  that  presence  of  mind  and  readiness  in  action  and 
promptness  in  expedients,  in  time  of  accident  or  of  emergency, 
which  is  hardly  less  necessary  than  on  the  battlefield.  In  still 
further  addition  to  these  requirements,  any  person  taking  charge 
of  boilers  must  understand  so  much  of  the  trades  of  the  boiler- 
maker  and  the  machinist  that  he  can  if  necessary  make  minor 
repairs,  reconstruct  his  feed-apparatus,  and  refit  the  valves.  He 
must  know  something  of  the  nature  and  of  the  peculiar  methods 
of  combustion  of  all  ordinary  fuels,  and  enough  of  the  principles 
of  combustion  to  be  able  to  realize  the  waste  that  may  follow  the 
introduction  of  an  excess  of  air  on  the  one  hand  or  the  produc- 
tion of  incomplete  combustion  on  the  other,  and  enough  of  the 
nature  and  dangers  of  sediment  and  incrustation  to  understand 
the  necessity  of  adopting  the  usual  expedients  for  prevention. 


THE   MANAGEMENT  AND    CARE    OF  BOILERS.  44! 

He  should  know  how  to  adjust  the  safety-valve,  and  should  un- 
derstand its  office  and  the  liability  to  accident  coming  of  its 
maladjustment  or  neglect. 

Intelligence,  experience,  and  conscientiousness  are  the  best 
and  only  real  insurance  against  accident. 

207.  Star  ing  Fires  is  an  art  which  is  not  always  familiar  to 
even  experienced  firemen.  With  the  soft  coals  it  is  only  neces- 
sary to  have  a  supply  of  some  kind  of  kindling  material  that 
can  be  lighted  by  a  match  or  a  lamp,  and  to  begin  by  building 
with  it  a  small  fire  and  then  adding  a  little  coal,  and  thus  grad- 
ually increasing  the  flame-bed  until  the  grate  is  fully  covered 
with  the  burning  fuel.  On  a  large  grate  the  whole  area  is  usually 
first  covered  with  fuel,  from  end  to  end  and  side  to  side,  so  that 
no  currents  of  air  can  enter  the  boiler  through  the  ash-pit,  and 
so  as  to  insure  that  all  air  entering  the  furnace  may  pass  over 
the  wood  used  in  kindling  the  fire.  The  wood  is  placed  on  the 
front  of  the  bed  of  coals,  with  oily  cotton-waste,  shavings,  small 
chips,  or  other  easily  ignited  material  under  it.  The  ash-pit 
doors  are  kept  closed  until  the  fire  is  fairly  burning,  so  that  the 
draught  may  be  concentrated  on  the  point  at  which  the  flame  is 
started.  After  a  few  minutes,  the  fire  being  well  started,  the 
upper  part  of  the  mass  burning  in  front  is  pushed  back  over  the 
grate,  and  the  flame  is  rapidly  communicated  to  the  whole  bed 
of  fuel.  When  this  is  effected  the  ash-pit  doors  are  opened  and 
the  fire  managed  in  the  customary  way.  The  precaution  must 
be  taken  to  see  that  the  air  has  free  access  to  the  boiler-room 
and  to  the  furnace. 

The  process  just  described  will  work  well  with  anthracite 
coal ;  but  the  operation  is  a  slower  one,  and  more  wood  is  usu- 
ally "required. 

Building  a  fire  of  wood  and  then  gradually  adding  coal  is  a 
more  expeditious  method  than  the  above,  but  it  is  less  econom- 
ical. 

When  it  is  known  that  steam  will  be  needed  the  boiler 
should  be  at  once  closed  up  and  filled,  in  order  that,  should  a 
leak  be  discovered  or  a  misfit  occur  in  setting  a  man-hole  or 
a  hand-hole  plate,  time  may  be  allowed  to  get  it  right  without 
causing  delay  in  getting  up  steam.  A  leak  discovered  after 


442  THE   STEAM-BOILER. 

steam  has  been  raised  may  sometimes  be  checked  by  driving  in 
pine  wedges.  The  rubber  "  gaskets"  used  in  making  the  joints 
under  man-hole  and  hand-hole  plates  may  be  "  blackleaded  "  on 
one  side  to  prevent  their  adhering  to  the  boiler.  All  valves 
should  be  carefully  examined  before  starting  fires,  and  especial 
care  should  be  taken  to  see  that  the  safety-valves  and  the  feed- 
check  valves  are  in  good  order.  All  flues  should  be  clean,  and 
every  part  of  the  boiler  and  all  its  accessories  should  be  given  a 
last  and  thorough  inspection. 

Before  starting  the  fires  the  precaution  should  be  taken  to 
see  that  the  fuel  is  not  allowed  to  be  placed  in  the  furnaces 
until  the  boilers  have  been  filled  with  water ;  even  the  kindling 
material  should  never  be  permitted  in  an  empty  boiler.  The 
fires  should  not  be  forced  at  the  first,  as  hot  gases  passing  over 
heating-surfaces  in  contact  with  cold  water,  and  the  sudden  ex- 
pansion due  to  too  rapid  increase  of  temperature,  may  cause 
strain  and  leakage. 

208.  The  Management  of  Fires  is  an  important  but 
often  neglected  branch  of  instruction  in  fitting  firemen  for  their 
special  duties.  The  economy  of  boiler  management  is  very 
largely  dependent  upon  the  skilful  handling  of  the  fuel  and  the 
furnace.  In  general,  the  fires  should  be  kept  of  even  thickness, 
clear  of  ash  and  clinkers,  and  as  clean  at  the  sides  and  in  the 
corners  as  elsewhere.  The  depth  of  the  fuel  is  determined  by  its 
nature  and  size  and  by  the  intensity  of  the  draught.  Hard  coals 
can  be  used  in  greater  depth  than  soft,  and  large  coal  in  deeper 
fuel-beds  than  small.  A  strong  draught  demands  a  thick  fire,  a 
mild  draught  a  thin  one.  With  a  low  chimney  and  natural  draught 
small  anthracite  or  fine  bituminous  coal  may  be  most  successfully 
burned  in  a  layer  but  a  hand's  breadth  in  thickness  ;  while  with 
large  "  steamboat"  coal  of  the  hardest  varieties  and  with  a  heavy 
forced  draught,  fires  have  been  actually  worked  successfully  of 
five  times  that  depth,  or  more.  The  secret  of  success  in  hand- 
ling fires  is  to  find  the  best  depth  of  fire  for  the  conditions 
existing ;  to  keep  that  thickness  at  all  times,  allowing  for  the 
ash  that  may  accumulate ;  to  throw  the  fuel  on  the  grate  at 
such  frequent  intervals  as  will  prevent  the  fire  burning  into 
holes  or  in  irregular  thickness  at  different  points ;  to  introduce 


THE   MANAGEMENT  AND   CARE   OF  BOILERS  443 

the  coal  so  quickly  and  with  such  exactness  of  direction  that  no 
serious  loss  may  occur  from  the  inrush  of  cold  air,  and  so  that 
every  shovelful  should  go  precisely  where  needed,  the  place 
for  the  next  shovelful  being  at  the  same  instant  located.  The 
removal  of  ash  is  best  done  by  means  of  a  rake  or  other  tool 
used  under  the  grate,  rather  than  by  stirring  and  breaking  up 
the  bed  of  fuel  by  working  through  the  furnace-door.  The 
various  forms  of  shaking  grate  now  in  use  are  often  very  effi- 
cient. For  best  working,  the  fire  should  usually  be  kept  bright 
beneath,  and  the  ash-pit  clear.  With  light  draught,  however, 
and  thin  fires,  it  is  sometimes  advisable,  if  sufficient  steam  can 
be  so  made,  to  allow  the  fire  to  be  less  frequently  raked  out, 
and  some  accumulation  of  ash  may  be  thus  produced  when 
working  with  maximum  economy. 

"  Firing,"  or  "  stoking,"  as  the  replenishing  of  the  fuel  is 
called,  must  be  done  very  quickly  and  skilfully  to  avoid  serious 
annoyance  by  variation  of  steam-pressure  and  supply.  Where 
several  furnaces  are  in  use  this  difficulty  is  less  likely  to  be  met 
with,  as  the  fires  may  be  cooled  and  cleaned  in  rotation.  A 
skilful  man  will  find  it  possible  to  keep  steam  very  steadily  with 
but  two  furnaces,  even. 

Ash-pits  should  not  be  allowed  to  become  filled  with  ashes, 
as  the  result  would  be  the  checking  of  the  draught,  the  reduc- 
tion of  the  steaming  capacity  of  the  boiler,  and  loss  of  efficiency, 
even  if  not  the  melting  down  of  the  grates.  It  is  customary 
at  sea  to  clean  out  the  ash-pits  and  send  up  ashes,  throwing 
them  overboard  once  in  every  watch  of  four  hours,  when  in  full 
steaming.  If  much  unburned  fuel  is  found  in  the  ashes,  it 
should  be,  if  possible,  cleaned  out  and  returned  to  the  fire,  or 
used  elsewhere. 

Cleaning  fires  consists  in  thoroughly  breaking  up  the  mass 
of  fuel  on  the  grate,  shaking  out  all  the  ashes,  quickly  raking 
out  all  "  clinker,"  as  the  semi-fused  masses  of  ash  and  fuel  are 
called,  and,  after  getting  a  level,  clean  bed  of  good  fuel,  as 
promptly  as  possible  covering  the  whole  with  a  layer  of  fresh 
coal.  This  is  done,  usually,  once  in  four  hours  at  sea  and  twice 
a  day  on  land ;  but  different  fuels  require  somewhat  different 
treatment.  The  work  should  be  performed  with  the  greatest 


444  THE   STEAM-BOILER. 

possible  thoroughness  and  dispatch,  to  avoid  serious  loss  of 
steam-pressure. 

Mr.  C.  W.  Williams'  instructions  for  handling  the  fires, 
where  bituminous  coal  is  used  and  an  air-supply  above  the  fuel 
is  provided,  are  substantially  as  follows : 

Charge  the  furnace  from  the  bridge-end,  gradually  adding 
fuel  until  the  dead-plate  is  reached  and  the  whole  grate  evenly 
covered.  Never  permit  the  fire  to  get  lower  than  four  or  five 
inches  in  thickness,  of  clear  and  incandescent  fuel,  uniformly 
distributed,  and  laid  with  especial  care  along  the  sides  and  in 
the  corners.  Any  tendency  to  burn  into  holes  must  be  checked 
by  filling  the  hollows  and  securing  a  level  surface.  All  lumps 
should  be  broken  until  not  larger  than  a  man's  fist.  Clean  out 
the  ash-pit  so  often  that  there  shall  be  no  danger  of  overheating 
the  grate-bars. 

An  ash-pit,  brightly  and  uniformly  lighted  by  the  fire  above, 
indicates  that  it  is  in  good  order  and  working  well.  A  dark  or 
irregularly  lighted  ash-pit  is  indicative  of  an  uncleaned  and 
badly  working  fire.  The  cleaning  of  the  fire  is  best  done,  in 
ordinary  working,  by  a  "rake"  or  other  tool  working  on  the 
under  side  of  the  grates,  and  not  by  a  " slice-bar"  driven  into 
the  mass  of  fuel  and  above  the  grate. 

209.  Different    Fuels    require    different    treatment.      The 
principles  just  stated  apply  generally,  but  more,  perhaps,  to  an- 
thracite coals.    The  soft  coals  are  commonly  so  disposed  on  the 
fire  that  a  charge  may  have  time  to  coke  and  its  gases  to  burn 
before  it  is  spread  over  the  grate ;  liquid  fuels  must  be  so  sup- 
plied  that  they  may  burn  completely,  at  a  perfectly  uniform 
rate,  and  especially  in  such  manner  as  to  be  safe  from  explosive 
combustion  ;  the  same  precaution  is  demanded  with  the  gaseous 
fuels.     Special  arrangements    of  grate    and   a  special    routine 
in  working  may  be,  and  often  are,  demanded  in  such  cases.* 

210.  The   Liquid  and  Gaseous  Fuels  are  often  and  suc- 
cessfully burned  in  conjunction  with  solid  fuels.     In  such  cases 
the  same  methods  are  to  be  adopted  and  precautions  observed 
in  handling  the  latter  as  when  burned  alone. 

*  For  the  peculiarities  of  these  fuels  and  their  use,  see  Chap.  III. 


THE   MANAGEMENT  AND   CARE    OF  BOILERS,  445 

The  liquid  fuels  are  almost  invariably  the  crude  petroleums. 
They  are  sometimes  burned  in  a  furnace  in  which  they  are 
allowed  to  drip  from  shelf  to  shelf  in  a  series  arranged  verti- 
cally at  the  front  of  the  furnace,  the  flame  passing  to  the  rear, 
with  the  entering  current  of  air  supporting  their  combustion. 
In  many  cases  they  are  sprayed  into  the  furnace  by  a  jet  of 
steam  which  should  be  superheated  and  at  high  pressure.  The 
use  of  the  steam  is  considered  to  have  a  peculiar  and  beneficial 
effect,  possibly  through  chemical  reactions  facilitating  the  for- 
mation of  hydrocarbons.  The  petroleums  are  all  liable  to 
cause  accident  if  carelessly  handled,  and  special  precaution 
must  be  observed  in  their  application  to  the  production  of 
steam. 

The  gaseous  fuels  are  seldom  used  under  steam-boilers,  except 
where  "  natural  "  gas  from  gas-wells  is  obtainable,  or  where  a 
very  large  demand  or  the  use  of  metallurgical  processes  justi- 
fies the  construction  of  gas-generators.  Even  greater  precau- 
tions against  accidents  by  explosion  are  needed  than  with  the 
liquid  fuels.  In  burning  gas,  maximum  economy  is  secured  by 
careful  apportionment  of  the  air-supply  to  the  gas-consump- 
tion, and  especially  in  avoiding  excess.  The  regenerator  sys- 
tem is  not  generally  economically  applicable  to  boilers. 

211.  The  Solid  Fuels,  coal  and  wood,  are  burned  in  fur- 
naces which  are  proportioned  especially  for  the  intended  fuel. 
With  soft  coals,  the  grate-bars  are  set  closer  together  than  for 
hard  coals ;  the  provision  for  the  introduction  of  air  above  the 
grate  is  larger,  and  a  "  dead-plate"  is  usually  provided  on  which 
to  coke  the  coal.     In  the  use  of  this  device,  the  fresh  fuel  is  piled 
on  the  dead-plate  at  the  furnace-mouth,  and  then  left  until  the 
next  charge  is  to  be  thrown  in  ;  the  first  is  then  pushed  in  and 
spread  over  the  fire,  and  the  second  charge  is  coked.     In  some 
cases  the  fuel  is  replenished   on  one  side  of  the  fire  at  a  time  ; 
but  oftener  it  is  spread  over  the  whole  surface  of  the  grate. 

A  furnace  for  burning  wood  is  deeper  than  one  intended  for 
coal.  Wood  burns  so  freely  that  the  ingoing  charges  must  be 
continually  replaced  by  fresh  fuel. 

212.  The  Operation  of  the  Boiler,  aside  from  the  man- 
agement of  the  fires,  in  such  manner  as  to  make  steam  regu- 


44-6  THE   STEAM-BOILER. 

larly  and  in  ample  quantity,  mainly  consists  in  adjusting  the 
draught  so  as  to  make  the  production  of  steam  keep  exact  pace 
with  the  demand,  and  in  keeping  the  supply  of  feed-water  as 
precisely  proportional  to  the  amount  demanded,  and  thus  pre- 
serving the  water  constantly  at  a  safe  level,  and  reducing  to  a 
minimum  the  danger,  on  the  one  hand,  of  uncovering  heating 
surfaces,  and  on  the  other  of  causing  heavy  "  priming"  or 
foaming,  or  the  production  of  wet  steam.  As  the  working 
conditions  of  a  steam-boiler  are  always  those  of  steady  motion, 
constant  vigilance  and  an  undisturbed  and  unconquerable  equi- 
librium of  mind  on  the  part  of  the  attendants  are  essential  to 
perfect  safety  and  thorough  efficiency. 

So  long  as  the  water  is  kept  at  the  proper  height  in  the 
boiler,  the  boiler  itself  being  in  good  repair,  safety  is  assured  ; 
and  if  the  steam-pressure  can  be  held  at  the  proper  point,  effi- 
ciency is  equally  well  insured  ;  but  to  maintain  a  state  of  abso- 
lute safety  and  efficiency,  it  is  essential  that  something  more 
than  careful  feeding  and  skilful  firing  be  practised.  Every 
apparatus  upon  which  the  working  of  the  boiler  is  in  any  de- 
gree dependent  must  be  known  to  be  in  good  order  and  abso- 
lutely reliable.  Feed-pumps  must  be  kept  in  good  repair,  well 
packed,  and  ready  for  service  on  the  instant ;  the  safety-valve 
must,  by  at  least  daily  trial,  be  seen  to  be  in  good  working 
order;  the  pressure-gauges  must  be  frequently  compared  with 
a  standard  test-gauge  to  make  certain  that  its  error — it  will 
usually  have  some  error — is  known  and  unimportant ;  and  the 
gauge-cocks  and  water-gauge  glass — the  latter,  especially,  is  lia- 
ble to  deceive — must  be  tried  often  and  their  reliability  made 
evident. 

Blow-off  and  feed  valves  often  leak,  must  be  often  exam- 
ined, and  should  be  repaired  or  reground  whenever  perceptibly 
affecting  the  water-supply.  A  grain  of  sand  or  a  chip  under 
a  valve  has  sometimes  given  rise  to  unfortunate  results. 

In  salt  water,  when  using  sea-water  in  the  boilers,  frequently 
blowing  off  from  the  bottom  or  a  continuous  discharge  from 
the  "  surface-blow"  or  "  scum-pipes"  is  essential  to  keeping  the 
water  so  fresh  as  not  to  produce  deposits  or  incrustation.  The 
higher  the  "  saturation"  permitted,  however,  provided  that 


THE   MANAGEMENT  AND    CARE    OF  BOILERS.  447 

common  salt  is  not  actually  deposited,  the  less  the  expense  of 
operation  and  the  less  the  amount  of  lime-scale  formed.  About 
twelve  times  the  quantity  of  salt  found  in  sea-water  is  thus 
the  maximum  ;  and  three  or  four  is  probably  as  high  as  is 
safe,  two  thirds  the  water  entering  the  boiler  being  converted 
into  steam,  the  remaining  third  blown  out  into  the  sea  again. 
And  generally,  if  ;/  represent  the  ratio  of  saltness  of  boiler  to 
that  of  the  sea,  and  m  the  ratio  of  feed-water  blown  out  to  that 
made  into  steam, 

i  i 

m  —  ;    n  •=. hi; 

n  —  i  m 

and  if  the  ratio  of  total  feed-water  to  total  evaporation  is/, 

m  +  i  n 

P '         i  n  —  I* 

If  large  boiler-power  is  demanded,  and  a  battery  consisting 
of  a  considerable  number  of  boilers  is  in  use,  one  man  should 
be  detailed  especially  to  see  that  the  water  is  properly  sup- 
plied ;  he  is  called  the  "water-tender."  On  a  large  steamer 
several  are  often  employed,  each  caring  for  a  set  of  boilers  and 
supervising  the  firemen  or  "  stokers"  and  coal-handlers  employed 
at  his  section.  All  these  workmen  should  be  carefully  chosen, 
and  known  to  be  skilful  and  trustworthy.  A  careless  or  unskil.- 
ful  man  will  waste  vastly  more  in  bad  firing  than  can  be  saved 
in  the  difference  of  wages  between  a  good  and  an  inefficient 
man.  One  good  man  should  handle  a  ton  of  coal  an  hour — sev- 
eral times  the  value  of  his  own  wages — the  total  charges  for  the 
boiler-room  amounting  usually  to  about  one  fourth  or  one  fifth 
wages,  three  fourths  or  four  fifths  fuel,  and  wear  and  tear.  The 
coal-handler  should  be  able  to  supply  two  to  four  firemen, 
according  to  distance  of  coal-bunkers  and  convenience  of  trans- 
portation. 

Firing — stoking — should  be  done  with  promptness  and  pre- 
cision during  a  few  seconds,  while  the  nearest  man  holds  the 
furnace-door  open.  Every  moment  of  needless  delay  allows 
great  volumes  of  cold  air  to  rush  into  the  furnace,  reducing  the 


448  THE    STEAM-BOILER. 

efficiency  of  the  boiler  and  causing  strain  by  cooling  the  sur- 
faces just  before  exposed  to  gases  of  high  temperature.  The 
damper  should  be  partly  closed  while  working  the  fire.  With 
a  number  of  furnaces  the  order  of  opening  the  furnace-doors 
may  be  systematically  arranged,  and  a  very  noticeable  saving 
thus  effected. 

213.  A  Forced    Draught    is   produced    by   the    use    of   a 
blower   or  fan,  or  by  the  steam-jet.     The  former   is  the   best 
method  where  practicable.     In  using  the  forced  draught,  the 
fires  should  be  managed  precisely  as  with  a  natural  draught ; 
but   the  rate  of  combustion  is  so  greatly  increased  that  they 
must  be  made  heavier,  and  the  process  of  replenishing  the  fuel 
even  more  carefully  conducted.     The  draught  should — indeed 
must — usually  be   checked   while   adding   fuel ;  but  where   the 
closed  fire-room  or  stoke-hole  is  adopted,  or  with  the  steam-jet, 
this  is  not  absolutely  necessary,  though  best  both  on  the  ground 
of  economy  and  of  safety.  When  the  blast  is  driven  into  the  ash- 
pit, care  should  be  taken  to  open  the  ash-pit  doors  the  instant 
the  fan  is  stopped,  or  danger  is  incurred  of  melting  down  the 
grate-bars  by  the  intense  heat  concentrated  beneath  them,  un- 
tempered  by  the  entering  current  of  cold  air. 

214.  Closed  and  Open  Boiler-rooms,  with  forced  draught, 
have  each  their  advantages  and  their  special  methods  of  man- 
agement.   With  the  closed,  air-tight,  fire-room  all  air  supplied  to 
the  fire  passes  through  the  room,  ventilating  it  thoroughly  and 
cooling  it,   while  at   the   same   time  enabling  the  fires  to  be 
worked  precisely  as  where  a  natural  draught  is  employed.     No 
peculiarities  of  management  are  introduced  other  than  come  of 
the  rapidity  of  combustion.     In  providing  for  the  opening  and 
closing  of  the  fire-room  doors  for  entrance  and  exit  of  the  at- 
tendants, a  double  system  must  be  so  arranged  that  one  will 
always  act  as  a  valve   to  close   communication   with  adjacent 
apartments.     In  putting  on  and  taking  off  the  blast  the  fan 
should  be  first  "  slowed  down,"  the  doors  then  opened,  and  finally 
the  blower  stopped.     In  putting  on  the  blast  these  steps  should 
be  precisely  reversed. 

With  the  open  boiler-room  and  closed  conducting  passages 
leading  from  fan  to  ash-pit,  the  special  precautions  to  be  taken 


THE   MANAGEMENT  AND    CARE    OF  BOILERS.  449 

are  simply  to  open  the  ash-pit  the  instant  the  blast  is  stopped, 
or  to  start  the  blower  the  instant  the  ash-pit  doors  are  shut. 

215.  The  Regulation  of  the  Steam-pressure  should  be 
effected  by  varying  the  intensity  of  the  draught  by  means  of 
the  damper  at  the  chimney,  or,  where  a  forced  draught  is  em- 
ployed, by  properly  adjusting  the  speed  of  the  blower;  it  should 
never  be  attempted,  except  in  a  serious  emergency,  to  regulate 
it  by  opening  furnace,   ash-pit,   or  u  connection"   doors.     The 
latter  method   is   certain    to    accelerate    corrosion,   strain   the 
seams,  and  produce  leakage  of  tubes,  as  well  as  to  waste  fueL 
The  rushing  of  currents  of  air,  alternately  cold  and  hot,  through 
the  flues  and  over  the  heating-surfaces  has  been  found  in  some 
cases  to  have  probably  been  the  cause  of  injury  leading  to  ex- 
plosion ;  and  the  introduction  of  cold  air  over  the  fire  is  invari- 
ably a  cause  of  serious  loss  of  economy  of  fuel. 

Automatic  dampers,  if  well  made  and  reliable,  are  very  use- 
ful. 

216.  The  Control  of  Water-supply  should  always  be  en- 
trusted only  to  experienced  and  proven  men ;  this  is  the  main 
precaution  to  be  taken  in  every  case.     The  more  uniform  the 
supply,  and  the  more  perfectly  the  proper  water-level  is  main- 
tained, the  safer  and  the  more  economical  the  operation  of  the 
boiler.     It  is  better  that  the  feed-water  be  supplied  continu- 
ously than  to  feed  intermittently.    Steam  is  then  made  more 
regularly,  and  of  better  quality ;  the  heating  of  the  feed  is  more 
steady  and  more  thorough  ;  the  boiler   itself  suffers  less  from 
varying  temperatures,  either  local  or  general ;  and  every  opera- 
tion goes  on  more  easily  and  more  satisfactorily. 

The  feed-pump,  if  used,  should  be  amply  large  for  cases  of 
emergency,  but  should  be  ordinarily  worked  continuously  and 
slowly  ;  the  injector,  if  employed,  should  be  of  such  size  that 
it  may  never  cease  working  while  the  boiler  is  in  normal  opera- 
tion ;  and  a  second  instrument  or,  better,  an  independent  feed- 
pump, should  be  always  ready  for  use  should  occasion  arise. 
The  necessity  for  watchfulness  is  greater  with  boilers  having 
small  water-space  for  their  power,  as  the  modern  tubular  and 
sectional  boilers,  than  in  the  older  types,  in  which  the  regulating 
effect  of  a  large  body  of  water  is  felt. 
29 


45°  THE   STEAM-BOILER. 

The  first  duty  of  engineer  or  of  fireman,  on  taking  charge 
of  a  boiler,  for  the  day  or  for  a  watch,  is  to  see  that  the  water 
is  at  the  right  height  ;  and  his  constant  care  throughout  the 
whole  period  for  which  he  is  responsible  is  to  keep  it  right,  and 
to  provide  against  any  contingency  that  may  introduce  a  liabil- 
ity of  its  rising  or  falling  beyond  the  intended  and  safe  range  of 
fluctuation. 

217.  Emergencies  are  liable  to  arise  unexpectedly  in  the 
operation  of  the  steam-boiler  and  demand  the  highest  qualities 
of  mind  and  character  on  the  part  of  him  who  may  be  called 
upon  to   meet   them.     Self-possession   and   coolness,  with   full 
control  of  every  faculty,  will   usually  enable  the  attendant  to 
successfully  meet  any  form  in  which  they  may  appear,  with  the 
single  exception   of  an  explosion  of  the  boiler  ;  for  that  case 
prevention  is  the  only  cure.     Minor  emergencies  occur  so  fre- 
quently that  the  experienced  engineer  or  fireman  will  generally 
meet  them  promptly  and  effectively,  and  greater  events  often 
find  him  equally  ready  and  prompt  of  action.      Every  attend- 
ant, whether  in  engine  or  boiler-room,  should  have  constantly 
in  mind  the  best  course  to  take  in  the  event  of  any  accident ; 
and  every  -intelligent  and  conscientious  man  will  have   often 
gone  over,  in  his  own  mind,  the  methods  and  means  by  which 
he  should  attempt   to  prevent  every  probable  accident,  or  to 
render  its  consequences  as  unimportant  as  possible.     There  is 
often  no  time  to  think,  and  whatever  is  to  be  attempted  can 
only  be  done  intuitively,  on  the  instant,  on  the  impulse  of  the 
moment,  guided  by  earlier  thought  or  earlier  experience.     This 
quality  of  readiness  in  emergencies  is  perhaps  the  most  valua- 
ble   of   all   those    especially  required    in   the    management    of 
engines,  boilers,  and  machinery  generally. 

218.  "  Low-water"  is  the   most  serious  and  trying  of  the 
conditions  liable  to  arise  in  steam-boiler  management.     Once 
the  water-level  has  fallen  below  that  of  the  crown-sheet  or  the 
upper  row  of  tubes,  but   one  thing  can  be  done — reduce  the 
temperature  of  the  furnace  and  flues  as  rapidly  as  possible  to  a 
safe  point.     To  introduce  a  larger  quantity  of  feed  might  cause 
a  sudden  and  dangerous  increase  of  pressure  by  flooding  the 
overheated  metal  ;  to  attempt  to  haul  out  the  fires  might  pro-- 


THE  MANAGEMENT  AND    CARE    OF  BOILERS.  451 

duce  a  similar  effect  by  the  momentarily  higher  temperature 
often  caused  by  breaking  up  the  bed  of  fuel,  and  by  the  pro- 
longed exposure  of  the  already  endangered  metal  it  might 
cause  the  hot  sheets  or  flues  to  give  way.  The  proper  course  to 
pursue  is  at  once  to  dampen  the  fires,  preferably  by  quickly 
covering  them  with  wet  ashes.  Coolness,  promptness,  and 
rapidity  of  action  are  the  only  safeguards  in  this  case.  With 
high  steam-pressure,  the  danger  is  that  the  overheated  and 
softened  and  weakened  sheets  may  be  forced  out ;  the  intro- 
duction of  the  feed-water  is  in  itself  a  less  serious  source  of 
danger.  The  Author  has  many  times,  in  experimental  work, 
pumped  water  into  a  red-hot  boiler,*  but  has  only  once  seen  an 
explosion  so  produced.  He  has  experimentally  allowed  the 
water  to  be  completely  evaporated  from  an  outside-fired  boiler, 
and  has  then  succeeded  in  covering  the  fires  with  ashes  and  re- 
filling the  boiler  without  injury.f  When  the  boiler  has  cooled 
down  and  no  steam  is  forming,  it  will  be  safe  to  blow  off  steam, 
then  haul  fires,  blow  out  the  water,  and  examine  to  see  if 
any  injury  has  occurred. 

Dangers  of  this  kind  rarely  arise  where  the  gauges  are  kept 
in  order;  but  carelessness  in  regard  to  the  water-gauges  and 
gauge-cocks  is  said  to  be  a  more  frequent  cause  of  accident  than 
all  other  causes  combined.  Equal  care  should  be  taken  to 
see  that  the  fusible  plugs,  if  used,  are  clean  and  in  good  condi- 
tion. 

219.  Priming  or  Foaming  takes  places  whenever  the  quan- 
tity of  steam  drawn  from  the  boiler  exceeds  that  which  can  be 
liberated,  dry,  from  the  mass  of  water  which  it  at  the  time 
contains.  This  action  may  be  due  either  to  forcing  the  boiler 
beyond  its  real  capacity,  or  to  the  presence  of  foreign  matters 
in  solution,  which  tend  to  cause  the  retention  of  the  bubbles  of 
steam  in  the  mass,  and,  when  leaving  it,  to  carry  spray  into  the 
steam-space.  A  boiler  will  foam  badly  if  the  design  and  con- 
struction are  such  that  a  rapid  circulation  is  not  insured,  sufficient 
to  carry  all  steam  made  below  the  upper  level  freely  to  the  sur- 


*  In  the  work  of  the  U.  S.  Commission  on  Steam-boiler  Explosions,  1875. 
\  This  might  not  be  as  safe  an  operation  with  an  inside  fired  boiler. 


45 2  THE   STEAM-BOILER. 

face,  where  it  may  be  naturally  discharged  ;  or  where  currents 
conflict ;  and  where  a  mass  of  water,  entangled  among  the  tubes 
or  flues,  finds  no  natural  way  of  egress,  laden  as  it  is  with  the 
steam  bubbles  which  convert  it  into  foam  ;  and  priming  may 
thus  occur,  even  when  the  boiler  is  working  well  within  its  rated 
capacity.  Any  boiler  will  foam  if  overworked. 

Priming  is  also  produced  by  the  presence  of  mucilaginous, 
oily,  or  other  foreign  matter  in  the  water ;  or  by  changing  from 
a  salt-water  feed  to  fresh-water,  and  sometimes  by  the  reverse  ; 
by  sudden  and  heavy  demand  for  steam  at  the  engine,  or  by 
suddenly  and  widely  opening  the  safety-valve ;  and  by  other 
causes  less  well  understood.  When  foaming  takes  place,  it  often 
throws  water  from  the  boiler  so  rapidly  and  in  such  quantities 
that  the  engine  may  be  liable  to  have  a  cylinder-head  knocked 
out,  and  the  height  of  the  water-level  in  the  boiler  may  be 
dangerously  lowered.  The  instant  such  dangers  arise  the  throt- 
tle-valve should  be  partly  closed,  when  the  water  will  usually 
immediately  settle  down  in  the  boiler,  making  it  possible  to 
ascertain  its  height  in  the  gauges.  If  dangerously  low, — a  rare 
occurrence,  however, — proceed  as  already  indicated  ;  if  other- 
wise, the  draught  should  be  promptly  lessened,  the  fires  checked, 
and,  by  thus  reducing  the  quantity  of  steam  made,  the  pro- 
duction of  foaming  and  its  attendant  dangers  may  be  quickly 
stopped.  If  the  cause  is  suspected  to  be  dirty  water,  contin- 
uous feeding  and  blowing,  and  thus  changing  the  water,  should 
be  resorted  to  to  remove  that  cause  of  danger.  With  boilers 
heavily  driven,  as  is  usual  at  sea,  and  too  common  elsewhere, 
priming  is  always  one  of  those  contingencies  which  those  in 
charge  of  the  boilers  must  be  prepared  to  meet.  Where  sur- 
face-condensers are  used  and  the  boiler  is  fed  with  water  of  un- 
changing and  pure  quality,  foaming  rarely  occurs. 

The  method  of  circulation  of  water  in  a  plain  cylindrical  or 
other  "  outside-fired  "  boiler,  and  the  course  of  the  steam  pro- 
duced, is  well  illustrated  in  the  accompanying  figure,  the  fire 
being  assumed  to  be  located  at  the  left.  The  greater  part  of 
the  steam  made  in  the  boiler  is  produced  immediately  over  the 
fire,  here  assumed  to  be  at  the  left,  and  rises  at  once,  as  seen, 
into  the  steam-space  above,  thus  determining  the  circulation 


THE   MANAGEMENT  AND    CARE    OF  BOILERS. 


453 


in  currents  rising  at  that  end  and  falling  at  the  rear  end  of  the 
boiler.  In  all  cases  the  rising  currents  are  at  the  hottest  part,  the 
descending  currents  at  the  cooler  portions  of  the  boiler.  Were 
a  boiler  so  constructed  as  to  be  uniformly  heated,  an  efficient  cir- 
culation would  not  be  obtainable. 

"  False  water"  is  a  term  applied  to  the  apparent  increase  of 
volume  of  the  water  in  a  boiler  when  priming  takes  place.  It 
may  be  imperceptible  ;  but  it  often  causes  an  apparent  rising  c  f 
the  water-level  to  the  extent  of  several  inches.  It  is  considered 
that  a  well-proportioned  boiler  should  be  capable  of  evaporating 
five  times  the  volume  of  its  own  steam-space  each  minute 


FIG.  117.— CIRCULATION  OF  WATER  AND  STEAM. 


without  serious  priming ;  but  it  is  not  thought  wise  to  attempt 
an  evaporation  exceeding  one  half  this  amount. 

220.  Fractures,  whether  of  seams,  sheets,  or  tubes,  are  liable 
to  occur  in  all  boilers;  but  the  danger  is  diminished  as  the  care 
taken  in  selection  of  material  is  the  greater,  the  construction 
better,  and  the  management  more  intelligent.  Such  injuries 
rarely  occur  so  suddenly  or  are  so  extensive  as  to  be  imme- 
diately dangerous,  and  ample  time  is  commonly  allowed  for  their 
detection  and  safe  remedy.  Cracks  in  sheets  or  seams  are  re- 
paired by  patching  and  in  tubes  by  plugging  each  end,  or  by  the 
removal  of  the  sheet  or  tube.  The  duty  of  the  attendant,  for 
the  moment,  is  to  reduce  steam-pressure  at  once,  and  as  soon 
as  possible  blow  off  steam,  to  empty  the  boiler  and  to  see  it 


454  THE   STEAM-BOILER, 

properly  repaired — temporarily  if  necessary,  but  preferably  per- 
manently.    A  blistered  sheet  should  be  treated  as  if  fractured. 

221.  A  Deranged  Safety-valve  may  sometimes  cause  dan- 
ger by  making  it  difficult  to   reduce  the  steam-pressure  or  to 
keep  it  below  a  dangerous  point.     This  is  sometimes  a  conse- 
quence of  the  rusting  of  the  stem  or  of  the  valve  and  its  sticking 
to  its  seat,  or  in  such  a  manner  that  an  insufficient  area  for  exit 
is  obtainable.     In  such  a  case  the  steps  to  be  taken  are  to  check 
the  fires,  to  reduce  the  production  of  steam,  and  to  find  other  di- 
rections of  egress,  as  through  gauge-cocks,  all  available  valves,  by 
the  engines  taking  steam  from  the  boiler,  and  by  means,  even, 
of  their  cylinder,  water,  and  drip  cocks,  until  the  safety-valve 
can  be  made  to  work  or  until  the  steam  can  be  disposed  of  in 
other  ways.     If  the  valve  be  daily  or  oftener  raised  to  its   full 
height,  no  such  danger  will  be  incurred. 

222.  The  General  Care  of  a  steam-boiler  demands  much 
experience,  some  knowledge  of  the  causes  and  the  methods  of 
prevention  and  of  remedy  of  injury,  and  thorough  reliability  on 
the  part  of  those  to  whom  it  is  entrusted.     Aside  from  the  in- 
juries and  the  deterioration  which  occur  in  its  daily  operation, 
there  are  others  which  are  to  be  anticipated  quite  independently, 
and  which  may  become  even  more  serious  when  the  boiler  is 
out  of  use  :  these  are  principally  the  various  forms  and  conse- 
quences of  corrosion.     Such  general  care  includes  the  preserva- 
tion of  the  boiler  against  decay  or  loss  of  efficiency,  the  reten- 
tion of  its  setting  in  good  repair,  and  the  keeping  in  order  of 
all  its  accessories  and  connections. 

223.  The  Chemistry  of  Corrosion  has  been  studied   by 
many  distinguished   modern  chemists,  and   is  now  well  under- 
stood.      Corrosion    of   iron  and    steel  and  the  changes  which 
characterize  that  method   of  deterioration  cannot  go  on  in  the 
air  except  when  both  moisture  and  carbonic  acid  are  present, 
or  unless  the  temperature  is  considerably  higher  than  that  of 
the  atmosphere.     When  exposed  to  the  action  of  free  oxygen, 
however,  under  either  of    these  conditions,  the  metal  is   cor- 
roded— rusts — rapidly    or    slowly,     according    to    its    purity. 
Wrought-iron  rusts  quickly  in  damp  situations,  and  especially 
when  near  decaying  wood  or  other  source  of  carbonic  acid  ; 


THE   MANAGEMENT  AND    CARE    OF  BOILERS.  455 

while  steels  are  corroded  with  less  rapidity,  and  cast-iron  is 
comparatively  little  acted  upon.  The  presence  of  acids  in  the 
atmosphere  accelerates  corrosion,  and  the  smoke  of  sulphur- 
charged  coal,  or  smoke  charged  with  pyroligneous  acid,  fre- 
quently causes  the  oxidation  of  out-of-door  iron  structures. 

The  composition  of  the  rust  forming  upon  surfaces  of  iron  is 
determined  by  the  method  of  oxidation,  but  is  principally  per- 
oxide of  iron.  Calvert  gives  the  following  : 

Rust  from  Conway  Bridge.  Llangollen. 

Fe2O3 93-094  92.900 

FeO 5.810  6.177 

Carbonate  of  iron 0.900  0.617 

Silica 0.196  0.121 

Ammonia traces  traces 

Carbonate  of  lime 0.295 

A  series  of  experiments  made  to  determine  the  effect  of  dif- 
ferent oxidizing  media,  after  four  months'  exposure  of  clean 
iron  and  steel  blades,  gave  results  *  indicating  that  oxidation  is 
principally  due  to  the  presence  of  carbonic  acid  with  oxygen. 

When  distilled  water  was  deprived  of  its  gases  by  boiling, 
and  a  bright  blade  introduced,  it  became  in  the  course  of  a  few 
days  here  and  there  covered  with  rust.  The  spots  where  the 
oxidation  had  taken  place  were  found  to  mark  impurities  in  the 
iron,  which  had  induced  a  galvanic  action,  precisely  as  a  mere 
trace  of  zinc  placed  on  one  end  of  the  blade  would  establish  a 
voltaic  current. 

224.  The  Methods  of  Corrosion  vary  with  circumstances. 
Kent  has  shown  f  that  the  rusting  of  iron  railroad  bridges  is 
sometimes  greatly  accelerated  by  the  action  of  the  sulphurous 
gases  and  the  acids  contained  in  the  smoke  issuing  from  the  lo- 
comotive, and  that  sulphurous  acid  rapidly  changes  to  sulphuric 
acid  in  the  presence  of  iron  and  moisture,  thus  greatly  acceler- 
ating corrosion.  Iron  and  steel  absorb  acids,  both  gaseous  and 
liquid,  and  are  therefore  probably  permanently  injured  when- 
ever exposed  to  them. 

Calvert  experimented  upon  iron  immersed  in  water  contain- 

*  Chemical  News,  1870-71.  f  Iron  Age,  1875. 


THE   STEAM-BOILER. 

ing  carbonic  acid,  in  sea-water,  and  in  very  dilute  solutions  of 
hydrochloric,  sulphuric,  and  acetic  acids.  A  piece  of  cast- 
iron  placed  in  a  dilute  acetic-acid  solution  for  two  years  was 
reduced  in  weight  from  15.324  grammes  to  3-3-  grammes,  and  in 
specific  gravity  from  7.858  to  2.631,  while  the  bulk  and  outward 
shape  remained  the  same.  The  iron  had  gradually  been  dis- 
solved or  extracted  from  the  mass,  and  in  its  place  remained  a 
carbon  compound  of  less  specific  weight  and  small  cohesive 
force.  The  original  cast-iron  contained  95  per  cent  of  iron 
and  3  per  cent  of  carbon,  the  new  compound  only  80  per  cent 
of  iron  and  11  percent  of  carbon.  Iron  immersed  in  water 
containing  carbonic  acid  was  also  found  to  oxidize  rapidly. 
Iron  exposed  to  the  wash  of  the  warm  aerated  water  of  the  jet- 
condensers  of  steam-engines  is  often  very  rapidly  oxidized,  and 
the  mass  remaining  after  a  few  years  often  has  the  appearance, 
texture,  and  softness  of  plumbago,  so  completely  is  the  iron  re- 
moved and  the  carbon  isolated. 

Mallett,  experimenting  for  the  British  Association,*  found 
the  rate  of  corrosion  of  cast-iron  greatly  accelerated  by  irregu- 
lar and  rapid  cooling,  and  retarded  by  a  slow  and  uniform  re- 
duction of  temperature  while  in  the  mould. 

The  rate  off  corrosion  is  usually  nearly  constant  for  long 
periods  of  time,  but  it  is  retarded  by  removal  of  the  coating 
formed  by  the  rust,  as  if  left  it  creates  a  voltaic  couple,  which 
accelerates  corrosion. 

Hard  iron,  free  from  graphite,  but  rich  in  combined  carbon, 
rusts  with  least  rapidity,  and  with  about  equal  rapidity  in  the 
sea  as  in  the  air,  in  an  insular  climate.  Two  metals  of  differ- 
ent character  as  to  composition  or  texture  being  in  contact,  the 
one  is  protected  at  the  expense  of  the  other.  Foul  sea-water, 
as  "  bilge-water,"  corrodes  iron  very  rapidly. 

The  rate  of  corrosion  of  iron  is  too  variable  to  permit  any 
statement  of  general  application.  In  several  cases  the  plates 
of  iron  ships  have  been  found  to  be  reduced  in  thickness  in 
the  bilges  and  along  the  keel-strake,  at  the  rate  of  0.0025  inch 
(0.06  millimetres)  per  year,  as  ordinarily  protected  by  paint ; 

*  Proc.  Inst.  C.  E.   1843. 


THE  MANAGEMENT  AND    CARE    OF  BOILERS. 


457 


while  it  is  stated  that  iron  roofs,  exposed  to  the  smoke  of  loco- 
motives, have  sometimes  lasted  but  four  years. 

The  iron  hulls  of  heavy  iron-clads  have  sometimes  been 
locally  corroded  through  in  a  single  cruise,  where  peculiarities 
of  composition  or  of  structure,  or  the  proximity  of  copper  or 
of  masses  of  iron  of  different  grade  or  quality,  had  caused  local 
action. 

225.  Durability  of  Iron  and  Steel. — Twaite*  gives  the  fol- 
lowing as  the  measure  of  the  probable  years'  life  of  iron  and 
steel  undergoing  corrosion,  assuming  the  metal  to  be  uniform 
in  thickness.  Thin  parts  corrode  most  rapidly. 


T= 


W 
~CL 


in  which  Wis  the  weight  of  the  metal  in  pounds,  of  one  foot 
in  length  of  the  surface  exposed  ;  L  is  the  length  in  feet,  of  its 
perimeter;  and  C  a  constant,  of  which  the  following  are  values  : 


VALUES  OF  c. 


MATERIAL  IN 

SEA  WATER. 

RIVER  WATER. 

IMPURE 
AIR. 

AVERAGE 
SEA  WATER. 

Foul. 

Clear. 

Foul. 

Clear,  or 
in  air. 

.0656 
.1956 
.1944 
.2301 
.0895 
copper,  o 
ass,  copp 

•0635 
•  1255 
.0970 
.0880 

•0359 
r  gun-brc 
;r,  or  gur 

.0381 
.1440 

•"33 
.0728 

•0371 
nze  
-bronze  . 

0113 
0123 
0125 
0109 
0048 

.0476 
•1254 
.1252 
.0854 
.0199 

Wrouerht-iron 

Steel  

Cast-iron   skin  removed  .... 

0.19  to  0.35 
0.30  to  0.45 

"        in  contact  with  brass, 
Wrought-iron  in  contact  with  br 

When  wear  is  added  to  the  effect  of  oxidization,  the  "life" 
of  a  piece  of  iron  or  steel  may  be  greatly  shortened.  If  kept 
well  painted,  multiply  the  result  by  two. 

The  mean  duration  of  rails  of  Bessemer  steel  is,  accord- 
ing to  experiments  in  Germany,  about  sixteen  years.  Ten 
years  of  trial  at  Oberhausen,  on  an  experimental  section  of  the 


*  Molesworth,  p.  32,  2ist  ed.,  1882. 


45$  THE   STEAM-BOILER. 

line  between  Cologne  and  Minden,  has  shown  that  the  renewals 
during  the  period  of  trial  were  76.7  per  cent  of  the  rails  of  iron 
of  fine  grain,  63.3  of  those  of  cementation  steel,  33.3  per  cent 
of  those  of  puddled  steel,  and  3.4  per  cent  Bessemer  steel. 

226.  The  Preservation  of  Iron  and  Steel  is  accomplished 
usually  by  painting,  sometimes  by  plating  it. 

As  the  more  porous  varieties  will  absorb  gases  freely  and 
some  liquids  to  a  moderate  extent,  Sterling  has  proposed  to  sat- 
urate the  metal  with  mineral  oil  ;  heating  the  iron  and  forcing 
the  liquid  into  the  pores  by  external  fluid  pressure,  after  first 
freeing  the  pores  from  air  by  an  air-pump,  or  other  convenient 
means  of  securing  a  vacuum  in  the  inclosing  chamber. 

Temperatures  of  300°  to  350°  Fahr.  (150°  to  177°  Cent.) 
and  pressures  of  i  D  to  20  atmospheres  are  said  to  be  sufficient 
for  all  purposes. 

Voltaic  action  may  be  relied  upon  to  protect  iron  against 
corrosion  in  some  situations.  Zinc  is  introduced  into  steam- 
boilers  for  the  double  purpose  of  preventing  corrosion  and  of 
checking  the  deposition  of  scale.  It  is  sometimes  useful  in  the 
open  air,  where  rusting  is  so  seriously  objectionable  as  to  justify 
the  use  of  so  expensive  a  preventive.  The  zinc  itself  is  often 
quickly  destroyed. 

Zinc  has  been  used  as  a  plating,  or  sheathing,  on  iron  ships,, 
as  by  the  plan  proposed  by  Daft,*  and  in  some  cases  with  good 
results. 

Mallett  has  proposed  the  use  of  lime-water  to  check  the 
internal  corrosion  of  the  bottoms  of  iron  ships  where  exposed 
to  the  action  of  bilge-water,  and  uses  a  solution  of  the  oxy- 
chloride  of  copper,  or  other  poisonous  metallic  salts,  in  the 
paint  applied  externally,  to  check  fouling  and  consequent 
oxidation;  the  amalgam  of  zinc  and  mercury  is  also  some- 
times used  to  protect  iron  plates. 

227.  The  Paints  and  Preservation  Compositions  in  use 
are  very  numerous  :  Coal-tar,  asphaltum,  and  the  mineral   oils 
are  all  used,  the  latter  having  the  advantage,  in  the  crude  state, 
of  being  free  from  oxygen  and  having  no  tendency  to  absorb  it, 

The  animal  and  vegetable  fats  and  oils  are  used  temporarily 
in  many  cases,  and  if  free  from  acid,  are  useful. 


THE  MANAGEMENT  AND    CARE   OF  BOILERS.  459 

Surfaces  of  iron  are  painted  with  red-lead  and  oil,  with  oxide 
of  iron  mixed  with  oil,  or  with  oxide  of  zinc  similarly  prepared. 

Sterling  prepares  a  varnish  by  dissolving  gum  copal  in 
paraffine  oil,  placing  the  iron  in  it,  and  heating  it  under  in- 
creased pressure.  Iron  vessels,  tinned  inside,  which  can  be  her- 
metically sealed,  are  used,  heated  by  superheated  steam.  Scott 
uses  the  following  mixture  : 

Coal  tar . . .    6  gallons. 

Black  varnish 3       " 

Wood-tar  oil 2       " 

Japanese  glue I       " 

Red  lead 28  Ibs. 

Portland  cement 14    " 

Arsenic „ 14    " 

The  Author  has  used  fish-oil  as  a  preservative  of  steam-boil- 
ers out  of  use  for  long  periods  of  time,  with  success,  and  has 
found  some  vegetable  paints  of  unknown  composition  far  more 
durable,  when  exposed  to  the  weather,  than  red-lead  and  oil. 

"  Iron  paints"  bear  heat  well,  and  are  often  better  than  any 
other  cheap  paint.  Iron  to  be  painted  should  first  be  carefully 
cleaned  by  scraping  and  washing,  and  then  coated  once  or  twice 
with  linseed-oil.  One  pound  of  good  oxide  of  iron  paint  should 
cover  20  square  yards  (16.7  square  metres)  of  iron. 

Where  practicable  the  Barff  method  of  protection  may  be 
adopted  for  small  parts.  It  consists  in  heating  the  iron  or  steel 
to  be  treated  to  a  temperature  of  500°  Fahr.  (260°  Cent.)  in  an 
atmosphere  of  steam,  and  thus  securing  an  even  and  imperme- 
able coating  of  the  black  (ferric)  oxide. 

Where  more  complete  protection  is  demanded,  the  iron  is 
heated  to  1200°  Fahr.  (649°  Cent.),  and  is  said  to  be  thus  made 
impregnable  against  the  attack  of  even  the  acrid  vapors  of  the 
chemical  laboratory. 

Steam-boilers  are  preserved,  in  mass,  against  corrosion  by 
various  special  methods.  They  are  sometimes  dried  thoroughly 
by  means  of  stoves,  if  necessary,  and  then  closed  up  with  a 
quantity  of  caustic  lime  in  their  water-bottoms  or  lower  water- 

*  Fouling  and  Corrosion  of  Iron  Ships.     London,  1867. 


460  THE   STEAM-BOILER. 

spaces.  Occasional  inspection  prevents  injury  occurring  unde- 
tected in  any  case. 

When  new  boilers  are  stored  they  are  usually  painted  inside 
and  out.  Air  should  be  excluded  from  them  by  closing  all 
man-holes,  etc.  Working  boilers  are  best  preserved  by  a  thin 
coating  of  scale  on  their  heating-surfaces.  Mineral  oils  being 
used  for  lubrication  of  their  engines,  decay  is  far  less  likely  to 
take  place  rapidly.  Steel  corrodes  more  rapidly  than  iron,  and 
the  common  brands  of  iron  corrode  less  than  the  finer.  Zinc 
placed  within  boilers,  and  in  amount  one  thirty-fifth  the  area  of 
the  heating-surface,  was  found,  by  the  British  Admiralty,  to  pro- 
tect them  perfectly.  A  pound  (0.45  kilogrammes)  of  carbon- 
ate of  soda  to  every  ton  (or  tonne]  of  coal  burned  is  ordered 
to  be  pumped  into  boilers  at  sea,  to  give  the  water  an  alka- 
line reaction.  Boilers  of  sea-going  vessels  average  a  life  of  nine 
or  ten  years. 

Boiler  Coverings  having  for  their  object  the  protection  of 
the  external  surfaces  against  loss  of  heat  and  from  any  inju- 
rious action  liable  to  occur  in  consequence  of  their  exposure, 
are  of  very  various  kinds,  and  are  always  considered  the 
better  the  more  perfect  they  are  as  non-conductors.  Care 
should  be  taken,  however,  that  they  do  not  themselves  cause 
injury  more  serious  than  that  which  they  are  designed  to  pre- 
vent. Hair-felt  has  been  known  to  cause — possibly  by  some 
peculiar  galvanic  or  electric  action — observable  acceleration  of 
corrosion  on  the  inner  sides  of  the  sheets  to  the  exterior  of 
which  it  has  been  applied,  as,  for  example,  where  used  to  cover 
the  steam-drums  of  marine  boilers;  mineral-wool,  when  con- 
taining sulphur-compounds,  has  been  known  to  absorb  moist- 
ure, and  to  thus  cause  rapid  corrosion  of  parts  with  which  it 
was  in  contact.  When  free  from  sulphur  no  such  danger  is 
incurred. 

The  experiments  of  Mr.  C.  E.  Emery  give  the  following  as 
the  relative  values  of  available  covering  materials :  * 


*  Trans.  Am.  Society  Mech.  Engrs.,  vol.  ii.,  1881. 


THE  MANAGEMENT  AND   CARE   OF  BOILERS. 


461 


Non-Conductor. 

Value. 

Non-Conductor. 

Value. 

Non-Conductor. 

Value. 

Wood-felt  

i  .000 

Charcoal  

.632 

Asbestos  

363 

Mineral-wool  No.  2... 
Do.  with  tar  
Sawdust  
Mineral-wool  No.  i... 

•  83* 
•  715 
.680 
.676 

Pine-wood  across  fibre. 
Loam,  dry  and  open... 
Slacked  lime  
Gas-house  carbon  

•553 
•550 
.480 
.470 

Coal-ashes  
Coke  in  lumps  
Air-space,  undivided 

•345 
.277 
.136 

Hair  or  wool  felt  is  injured  by  high  temperature  ;  woods  are 
liable  to  char,  and  all  organic  matters,  in  presence  of  grease  and 
dampness,  to  take  fire  spontaneously.  Asbestos  is  much  used, 
as  is  also  "  rock-wool,"  which  is  less  likely  to  absorb  moisture 
than  the  "  mineral-wool  "  from  the  blast-furnaces.  Sand,  ashes, 
and  other  earthy  matters  are  often  used  to  fill  in  over  boilers. 
They  are,  however,  liable  to  conceal  and  accelerate  corrosion 
whenever  leakage  takes  place  beneath  them.  In  all  cases  the 
values  of  successive  layers  of  non-conductor  decrease  in  a 
geometric  ratio.  Anything  that  will  encage  air  in  its  pores  is  a 
good  covering.  Large  boilers  and  their  pipes,  as  designed  by 
Mr.  E.  D.  Leavitt,  Jr.,  were  covered  with  about  two  inches  and 
a  half  of  plaster  and  sawdust,  and  one  inch  of  hair-felt  outside 
that.  The  proportion  of  the  mixture  is  about  one  part  of 
plaster  and  two  parts  of  sawdust.  The  plaster  and  the  sawdust 
are  mixed  up  like  mortar.  They  are  first  put  in  together  dry, 
and  then  wet  and  mixed  up.  For  steam-pipes,  the  mixture  is 
applied  from  one  and  a  half  to  two  and  a  half  inches  thick. 

For  boilers,  wooden  battens  f  by  2|-  inches  wide  are  used. 
Between  the  edge  of  the  batten  and  the  boiler  half  an  inch  of 
the  compound  is  put.  These  are  fastened  all  around  the  boiler , 
then  a  band  of  hoop-iron  is  put  around  it,  and  filled  between  the 
battens  with  plaster.  The  practice  of  putting  it  on  in  little 
blocks  about  a  foot  square  has  been  adopted.  Outside  of  that, 
the  specifications  call  for  an  inch  of  hair-felt  and  canvas.* 

228.  Leakage,  and  contact  of  damp  portions  of  supports 
and  setting,  produce  the  most  serious  corrosion.  A  leak,  once 
started,  will  keep  everything  near  it  damp,  and  thus  cause 
acceleration  of  oxidation  to  a  very  marked  degree.  Where  the 
leakage,  or  the  dampness  produced  by  it,  finds  its  way  between 
the  iron  of  the  boiler  and  the  brickwork  about  it,  there  is  no 


*  Trans.  Am.  Soc.  Mech.  Engrs.,  1882. 


THE    STEAM-BOILER. 

opportunity  of  evaporation  and  drying  the  moistened  surfaces, 
and  the  dampness  thus  held  in  contact  with  the  metal  promotes 
decay.  When  inspecting  the  boiler,  care  should  be  taken  to 
detect  every  such  cause  of  deterioration,  and  to  immediately 
repair  the  injured  part.  It  is  well  to  so  design  and  construct 
the  boiler  that  there  will  be  as  little  liability  as  possible  to  this 
kind  of  injury. 

229.  Galvanic   Action  is  liable  to  occur,  and  enormously 
to  accelerate  corrosion,  either  local  or  general,  whenever  a  mass 
of  brass,  bronze,  or  copper,  large  or  small,  is  in  metallic  contact 
with  the  boiler  at  any  point,  or  with  any  of  its  connections. 
The  brass  tubes  of  a  surface-condenser  have  been  often  known 
to  thus  cause  the  ruin  of  a  boiler  in  a  few  months,  and  very 
serious  general  corrosion  in  few  weeks.     Copper  boiler-tubes, 
brass   valve-seats,   and    any   other   minor  part    made    of   such 
electro-negative  metals,  may  similarly  cause  local  deterioration 
and  leakage  or  weakness.     The  remedy  is  either  to  remove  the 
cause   of   the  trouble ;  to   protect    the  metal   attacked,  as   by 
allowing  it  to  become  coated  with  a  thin  layer  of  incrustation ; 
or  to  counteract  the  effect  of  the  electro-negative  metal  by  in- 
troducing a  mass  of  another  element,  as  zinc,  which  is  electro- 
positive to  both  the  iron  of  the  boiler  and  the  copper  or  other 
material  producing  the  destructive  action.     In  the  latter  case, 
the  zinc  will  be  corroded  instead  of  the  iron  of  the  boiler,  and 
must  be  occasionally  renewed. 

230.  Incrustation  and  Sediment  are  deposited  in  boilers, 
the  one  by  the  precipitation  of  mineral  or  other  salts  previously 
held  in  solution  in  the  feed-water,  the  other  by  the  deposition 
of  mineral  insoluble  matters,  usually  earths,  carried  into  it  in 
suspension  or  mechanical  admixture.     Occasionally  also  vege- 
table matter  of  a  glutinous  nature  is  held   in  solution  in  the 
feed-water,  and,  precipitated  by  heat  or  concentration,  covers 
the  heating-surfaces  with  a  coating  almost  impermeable  to  heat 
and  hence  liable  to  cause  an  overheating   that   may  be  very 
dangerous  to  the  structure.     A  powdery  mineral  deposit  some- 
times met  with  is  equally  dangerous,  and  for  the  same  reason. 
The  animal  and  vegetable  oils  and  greases  carried  over  from  the 
condenser  or  feed-water  heater  are   also  very  likely  to   cause 


THE  MANAGEMENT  AND   CARE    OF  BOILERS,  463 

trouble.  Only  mineral  oils  should  be  permitted  to  be  thus  in- 
troduced, and  that  in  minimum  quantity.  Both  the  efficiency 
and  the  safety  of  the  boiler  are  endangered  by  any  of  these  de- 
posits. 

The  amount  of  the  foreign  matter  brought  into  the  steam- 
boiler  is  often  enormously  great.  A  boiler  of  100  horse-power 
uses,  as  an  average,  probably  a  ton  and  a  half  of  water  per 
hour,  or  not  far  from  400  tons  (406  tonnes)  per  month,  steaming 
ten  hours  per  day,  and,  even  with  water  as  pure  as  the  Croton 
at  New  York,  receives  90  pounds  (41  kgs.)  of  mineral  matter, 
and  from  many  spring  waters  a  ton  (1.016  tonnes],  which  must 
be  either  blown  out  or  deposited.  These  impurities  are  usu- 
ally either  calcium  carbonate  or  calcium  sulphate,  or  a  mixture; 
the  first  is  most  common  on  land,  the  second  at  sea.  Organic 
matters  often  harden  these  mineral  scales,  and  make  them  more 
difficult  of  removal. 

The  only  positive  and  certain  remedy  for  incrustation  and 
sediment  once  deposited  is  periodical  removal  by  mechanical 
means,  at  sufficiently  frequent  intervals  to  insure  against  injury 
by  too  great  accumulation.  Between  times,  some  good  may 
be  done  by.  special  expedients  suited  to  the  individual  case. 
No  one  process  and  no  one  antidote  will  suffice  for  all  cases. 

Where  carbonate  of  lime  exists,  sal-ammoniac  may  be  used 
as  a  preventive  of  incrustation,  a  double  decomposition  occur- 
ring, resulting  in  the  production  of  ammonium  carbonate  and 
calcium  chloride — both  of  which  are  soluble,  and  the  first  of 
which  is  volatile.  The  bicarbonate  may  be  in  part  precipitated 
before  use  by  heating  to  the  boiling-point,  and  thus  breaking 
up  the  salt  and  precipitating  the  insoluble  carbonate.  Solu- 
tions of  caustic  lime  and  metallic  zinc  act  in  the  same  manner. 
Waters  containing  tannic  acid  and  the  acid  juices  of  oak,  su- 
mach, logwood,  hemlock,  and  other  woods,  are  sometimes  em- 
ployed, but  are  apt  to  injure  the  iron  of  the  boiler,  as  may  acetic 
or  other  acid  contained  in  the  various  saccharine  matters  often 
introduced  into  the  boiler  to  prevent  scale,  and  which  also 
make  the  lime-sulphate  scale  more  troublesome  than  when  clean. 
Organic  matters  should  never  be  used. 

The  sulphate  scale  is  sometimes  attacked  by  the  carbonate 


464  THE    STEAM-BOILER. 

of  soda,  the  products  being  a  soluble  sodium  sulphate  and  a 
pulverulent  insoluble  calcium  carbonate,  which  settles  to  the 
bottom  like  other  sediments  and  is  easily  washed  off  the  heat- 
ing-surfaces. Barium  chloride  acts  similarly,  producing  barium 
sulphate  and  calcium  chloride.  All  the  alkalies  are  used  at 
times  to  reduce  incrustations  of  calcium  sulphate,  as  is  pure 
crude  petroleum,  the  tannate  of  soda,  and  other  chemicals. 

Marine  boilers  have  been  effectively  treated  for  the  preven- 
tion or  the  removal  of  scale,  by  introducing  sheet-zinc,  or  zinc 
in  balls  or  in  blocks  of  any  convenient  size  and  form.  The  in- 
crustation met  with  in  marine  boilers,  properly  managed,  being 
always  nearly  pure  sulphate  of  lime,  the  zinc,  probably  by  some 
voltaic  action,  causes  the  deposit  to  become  pulverulent,  in- 
stead of  compact,  and  very  hard  and  strong,  as  when  formed  in 
the  unprotected  boiler,  and  it  also  compels  the  precipitation  of 
the  mineral  upon  the  zinc  itself  principally.  The  water  in  boil- 
ers of  any  kind  is  very  liable  at  times  to  become  acidified  per- 
ceptibly by  the  decomposition  of  the  lubricants  entering  with 
the  feed-water  from  the  engine  cylinders  and  condensers,  and 
corrosion  is  thus  accelerated.  In  such  cases  the  zinc  suffers 
and  the  boiler  is  preserved,  if  metallic  contact  is  secured  be- 
tween the  iron  or  steel  and  the  zinc — precisely  as,  when  the 
boiler  itself  is  constructed  of  different  qualities  of  metal,  one 
part  is  preserved  while  another  part  is  corroded.  Zinc,  as, 
relatively,  an  electro-positive  metal,  protects  iron  ;  which  latter 
is  electro-negative  to  the  former,  and  takes  the  hydrogen  of  so 
much  water  as  may  be  decomposed  by  the  voltaic  action  occur- 
ring, the  zinc  being  attacked  by  the  oxygen  set  free  on  that 
element  of  the  voltaic  pile  so  formed.  Marine  boilers  thus 
protected  have  shown  no  trace  of  decay  after  years  of  use. 

Whenever  zinc  is  used,  the  precaution  should  be  taken  to 
secure  a  perfect  metallic  connection  between  it  and  the  boiler ; 
otherwise  it  will  be  neither  uniform  in  action  nor  reliable.  The 
zinc  is  sometimes  amalgamated  to  prevent  wasteful  oxidation  by 
local  action. 

A  little  soda,  or  sodium  carbonate,  introduced  into  the 
boiler  may  often  insure  the  formation  of  a  softer  deposit  where 
it  is  found  to  be  hard,  and  to  so  incrust  and  embalm  the  zinc 


THE  MANAGEMENT  AND    CARE    OF  BOILERS.  465 

that  it  ceases  to  do  its  work.  A  surface  of  zinc  of  25  to  50 
square  inches  (2.5  to  4.5  square  decimetres,  nearly)  per  ton  of 
water  contained  in  the  boiler,  and  per  month,  is  usually  found 
ample. 

After  studying  the  use  of  zinc  as  an  "  anti-incrustator,"  and 
the  reports  of  M.  Lesueur,  who  first  introduced  it  extensively 
in  France,*  M.  Euvrard  concludes  that  it  should  be  used  in  the 
form  of  "  pigs"  or  ingots,  and  in  any  type  or  in  any  part  of  a- 
boiler,  although  it  is  better  not  to  place  it  on  the  heating-sur- 
faces of  the  firebox.  He  advises  from  one  pound  to  two  pounds 
for  every  ten  square  feet  of  heating-surface  at  a  time  (-J-  to  I 
kg.  per  sq.  m.).  It  is  found  that  zinc  is  valuable  with  calcareous 
feed-waters  when  not  excessively  hard,  causing  the  deposit  to 
become  pulverulent,  and  thus  altering  an  incrustation  or  scale 
into  a  sediment. 

Water-tube  Boilers  have  been  successfully  treated  by  M. 
C.  Quehaut,f  where  the  incrustation  was  calcareous,  and  largely 
consisting  of  calcic  sulphate,  by  using  instead  of  the  "  tartri- 
fuges"  commonly  employed  for  such  cases,  none  of  which 
proved  satisfactory,  sheet-zinc  of  thickness  No.  18.  Sheet? 
about  two  metres  (6.56  feet)  long  and  0.8  metre  (3  feet)  wide 
were  cut  into  strips  each  about  y1^-  metre  (3.28  inches)  wide, 
and  wrapped  helically  on  a  mandril,  forming  coils  of  which 
about  45  kilograms  (100  pounds)  were  introduced  into  a  boiler 
rated  at  40  horse-power  at  each  charge.  The  making  of  the 
coils  cost  about  one  dollar.  One  of  the  strips  so  coiled  was 
pushed  into  each  tube  after  each  cleaning,  and  withdrawn  at 
the  succeeding  period  of  washing  out.  Heavier  zinc  did  not 
answer  as  well,  as  the  strips  were  liable  to  be  displaced  by  the 
circulating  current. 

Incrustation  takes  place  on  the  zinc  instead  of  upon  the 
adjacent  iron  surfaces.  It  is  pulverulent,  and  easily  removed. 
The  cost  was  $2.50  per  annum  per  horse-power. 

231.  Repairs  are  the  source  of  the  great  expense  of  main- 
tenance of  steam-boilers,  and  sometimes  of  new  dangers  hardly 
less  serious  than  those  which  they  are  expected  to  prevent, 

*  Annales  des  Mines,  1877;  Jour.  Franklin  Inst.  1878. 
f  Ann.  de  1'Association  des  Ingenieurs  de  Liege,  4tne  serie,  t.  v.,  1886.. 
30 


466  THE    STEAM-BOILER. 

Frequent  and  systematic  inspection  and  test  will  always  reveal 
the  approaching  necessity  of  repairs  long  before  serious  risks 
are  run,  and,  if  promptly  attended  to  and  skilfully  performed, 
the  life  of  the  boiler  may  often  be  very  greatly  prolonged.  At 
sea  it  is  customary  to  have  on  hand  a  good  stock  of  extra 
boiler-plate,  rivets,  tubes,  and  other  material  for  use  in  making 
repairs,  and  to  have  all  minor  and  temporary  repairs  made  by  the 
engineer's  crew.  On  land  this  is  rarely  necessary,  as  boiler- 
makers  are  usually  close  at  hand,  and  the  work  can  be  done 
more  perfectly,  quickly,  and  cheaply  by  regularly  employed 
workmen. 

Leaky  tubes  are  often  plugged  until  it  becomes  convenient 
to  replace  them  by  new  ones.  In  such  cases  wooden  or  iron 
plugs  are  driven  into  the  ends,  and  leakage  thus  checked. 
Sometimes  special  apparatus,  devised  with  a  view  to  con- 
venience of  application  while  steam  is  still  kept  on,  are  em- 
ployed. Local  defects,  as  oxidation  or  blisters,  are  remedied 
by  bolting  on  "  soft-patches"  of  boiler-plate  fitted  to  the  weak- 
ened surface  and  made  tight  by  a  cement  of  red-lead  and  oil, 
or  a  mixture  of  red  and  white  lead  and  oil,  with  iron  borings 
and  some  other  constituent,  as  sal-ammoniac,  the  effect  of  which 
is  to  promote  the  oxidation  of  the  borings  and  the  production 
of  a  hard,  stone-like  cement.  A  permanent  "  job"  is  made  by 
cutting  out  the  defective  metal,  and  riveting  in  a  piece  of  new 
boiler-plate,  thus  making  a  "  hard-patch."  A  patch  secured  by 
tap-bolts  is  also  sometimes  called  a  "  hard-patch/' 

Leaks  in  steam-pipes  are  stopped  by  placing  sheet-rubber 
packing  over  the  crack  or  joint,  covering  this  with  sheet  copper 
or  brass,  and  wrapping  with  tightly  wound  wire  or  cord.  Feed- 
pipes may  be  similarly  temporarily  repaired,  or  by  covering  the 
leak  with  a  "  putty"  of  red  and  white  lead  and  wrapping  it  with 
canvas  and  twine. 

Where  a  crack  appears  in  any  part  of  the  heating-surface,  if 
not  more  than  two  or  three  inches  long,  it  should  be  stopped 
by  drilling  at  each  end  and  inserting  a  screw-plug.  A  long 
crack  must  be  patched.  Hard-patches  are  used  when  in  con- 
tact with  the  fire  ;  soft-patches  elsewhere  : 

232.   Inspection  and  Tests  of  strength   should   be  occa- 


THE  MANAGEMENT  AND    CARE   OF  BOILERS.          467 

sionally  resorted  to  for  the  purpose  of  determining  the  precise 
condition  of  the  boiler  at  the  time,  and  its  absolute  safety  under 
the  conditions  of  its  regular  use.  Custom  and  opinion  differ 
somewhat,  among  the  ablest  and  most  experienced  engineers, 
as  to  the  precise  method  and  the  extent  to  which  such  exami- 
nations and  tests  should  be  carried.  It  may  be  safely  assumed, 
however,  that  the  following  principles  and  processes  will  be 
considered  as,  at  least,  on  the  safe  side. 

The  complete  visual  inspection  and  examination  of  a  boiler, 
inside  and  out,  should  be  considered  one  of  the  primary  duties 
of  the  person  responsible  for  its  safe  operation  at  every  avail- 
able opportunity,  and  during  its  operation  a  watchful  eye 
should  be  kept  upon  it  uninterruptedly.  With  marine  boilers, 
a  complete  examination  is  expected  to  be  made  every  time  that 
steam  is  off — usually  at  the  end  of  every  trip ;  stationary  and 
locomotive  boilers  are  inspected  at  regular  intervals  by  skilled 
inspectors  or  by  the  master-mechanic  having  charge  of  them. 
The  former  should  be  so  examined  at  least  once  in  each  three 
months,  and  a  complete  inspection  and  thorough  test  should 
be  made  as  often  as  once  a  year ;  the  latter  still  oftener  de- 
mands attention. 

In  a  careful  inspection,  the  inspector  goes  underneath  and 
examines  all  the  fire-sheets,  and  inside  and  with  hammer  and 
chisel  and  lamp  examines  every  portion  of  the  boiler.  If  a 
corroded  or  grooved  place  is  found,  or  a  blister,  it  receives  care- 
ful attention.  If  for  any  reason  the  examination  should  be 
made  more  complete,  the  hydrostatic  test  is  applied.  In  the 
course  of  the  examination,  the  safety-valves,  the  gauge-cocks, 
water-gauges,  feed  and  stop  valves,  pumps,  dampers,  every  de- 
tail, should  receive  careful  attention.  The  tap  of  the  hammer 
will,  to  the  experienced  ear — and  inspection  should  only  be 
intrusted  to  experienced  men — reveal  the  thickness  of  a  sheet, 
the  presence  of  a  crack,  groove,  or  any  form  of  serious  oxida- 
tion or  injury,  the  soundness  of  stays  and  braces  and  their  con- 
nections, and  the  nature  and  extent  of  any  defect  that  may 
exist.  After  this  inspection  the  defects,  if  any,  are  removed, 
and  after  the  repairs  are  completed  the  inspection  should  be 
repeated  to  make  sure  that  the  work  has  all  been  done,  and 


468  THE   STEAM-BOILER. 

properly  done.  Finally,  the  boiler  is  closed,  filled  to  the  safety- 
valve,  all  stop-valves  being  closed,  and  is  subjected  to  a  pres- 
sure exceeding  its  working  pressure  by  at  least  one  half,  and 
preferably  more.  Many  authorities  advise  a  double  pressure. 
While  this  operation  is  going  on,  the  inspector  carefully 
watches  to  see  that  no  new  weakness  is  revealed. 

That  testing  by  hydraulic  pressure  is  not  alone  sufficient  to 
reveal  dangerous  defects  or  to  insure  against  disaster  is  un- 
questionable. The  Author  has  repeatedly  met  with  evidence 
that  explosions  have  occurred  at  pressures  less  than  those  at 
which  tests  had  been  made ;  and  it  is  well  known  to  experienced 
engineers,  and  especially  to  inspectors,  that  a  dangerously  thin 
boiler  may  sustain  high  pressures  for  a  time.  A  case  is  related  * 
in  which  a  water-pressure  of  12  atmospheres  was  sustained  by  a 
boiler  which  in  places  was  exceedingly  thin,  and,  as  reported, 
at  several  points  not  thicker  than  paper.  It  not  infrequently 
occurs  that  the  inspector's  hammer  is  driven  through  sheets  by 
which  very  considerable  pressures  had  been  sustained. 

It  was  at  one  time  common  to  test  boilers  to  three  times 
their  working  pressure,  or  even  more  ;  but  it  is  less  usual  now. 
The  United  States  regulations  controlling  steam-vessels  pre- 
scribe a  ratio  of  i^-  to  i  ;  French  regulations  direct  that  a  ratio 
of  2  to  I  shall  be  adopted  for  new  boilers,  annually,  on  naval 
vessels,  and  the  same  on  merchant  vessels  at  first,  but  later  re- 
duced the  ratio  to  i£  to  I,  although  even  then  this  pressure 
must  not  be  kept  up  more  than  five  minutes.f  The  British 
regulations  prescribe  2  to  I,  the  tests  to  be  made  semi -annual- 
ly. If  signs  of  weakness  are  observed  the  pressure  may  be  re- 
duced. All  boilers  should  be  drilled  occasionally  wherever 
thinness  of  plate  is  suspected.  All  such  tests  and  inspections 
should  be  made  before  painting,  and  inspection  should  be  made 
while  the  boiler  is  still  under  the  test-pressure.  Leaks  are 
often  more  easily  detected  under  cold  water  than  under  steam- 
pressure  ,  and  the  inspection  rather  than  the  test  is  the  insur- 
ance against  accident.  This  inspection  and  the  hammer-test 
are  especially  relied  upon  where  the  boiler  is  one  with  the  his- 

*  Locomotive,  Sept.  1873,  p.  3. 

f  Ledieu,  Appareils  a  Vapeur,  vol.  ii. 


THE   MANAGEMENT  AND    CARE    OF  BOILERS.          469 

tory  of  which  the  inspector  is  unfamiliar,  and  when  old  and 
worn ;  as  it  is  only  by  this  plan  that  cracks,  leaks,  blisters,  dis- 
tortion of  parts,  and  corrosion  can  be  satisfactorily  found  and 
gauged. 

All  boilers  are  usually  very  carefully  inspected  inside  and 
out  at  least  once  a  year,  and  thoroughly  tested.  It  is  custom- 
ary to  make  quarterly  examinations  also  as  complete  as  possi- 
ble, but  not,  as  a  rule,  to  make  the  extended  inspection  and 
test  which  is  insisted  upon  at  the  annual  inspection.  Where 
the  feed-wafer  is  impure,  however,  and  where  sediment  and  in- 
crustation are  found  to  give  occasion,  these  periodical  examina- 
tions should  be  made  so  frequently  that  all  possible  danger  may 
be  avoided.  Every  boiler  should  be  cleaned  out  and  thor- 
oughly freed  from  incrustation  at  intervals — whether  a  year,  a 
month,  or  a  week — such  as  will  secure  immunity  from  danger 
of  overheating  and  from  serious  loss  of  economy. 

233.  General  Instructions  for  the  management  and  care  of 
boilers  should  always  be  written  out  and  placed  in  the  hands 
of  attendants  whenever  they  are  not  known  to  be  in  every  re- 
spect familiar  with  their  duties.  Especially  should  they  be 
cautioned  against  raising  steam  too  rapidly,  or  emptying  the 
boiler  while  the  setting  is  hot,  and  against  pumping  cold  water 
in  large  quantities  into  a  hot  boiler,  and  other  errors  of  either 
omission  or  commission  by  which  the  boilers  may  be  injured. 
All  air-leaks  about  the  setting  should  be  found  and  stopped. 
The  most  perfect  cleanliness  should  be  enjoined. 

The  most  complete  codes  of  instructions  are  those  issued  to 
naval  officers,  of  one  of  which  the  following  is  an  abstract  :* 

The  engineer  officers  are  to  make  themselves  acquainted 
with  the  general  construction  and  with  any  special  fitting  of  the 
boilers  under  their  care.  In  order  to  protect  the  plates  and 
stays  from  corrosion,  it  is  essential  that  the  interior  surfaces 
should  be  coated  with  some  impervious  substance.  A  thin 
layer  of  hard  scale,  deposited  by  working  the  boilers  with  sea- 
water,  has  been  found  to  be  the  most  effectual  preservative ; 
and  therefore  all  boilers  when  new,  or  at  any  time  when  any  of 


*  London  Engineering,  1884. 


470  THE   STEAM-BOILER. 

the  plates  or  stays  are  bare,  are  to  be  worked  for  a  short  time 
with  the  water  at  a  density  of  about  three  times  that  of  sea- 
water,  until  a  slight  protective  scale  has  been  deposited ;  but 
in  this  case  care  is  to  be  taken  not  to  allow  a  scale  to  be  formed 
of  such  a  thickness  as  would  in  an  appreciable  degree  impair 
the  efficiency  and  economy  of  the  boilers.  During  the  first 
six  months'  service  the  boilers  should  be  frequently  examined ; 
and  afterwards,  where  possible,  at  least  once  a  month,  or  after 
steaming  twelve  days.  The  boilers  are  to  be  examined  care- 
fully after  steaming  ;  and  every  judicious  measure  is  to  be  used 
for  the  prevention  and  removal  of  scale,  especially  on  the  fur- 
nace crowns  and  sides.  Whenever  serious  corrosive  action  has 
been  discovered  it  is  to  be  at  once  reported,  together  with  full 
information  as  to  the  circumstances  and  the  supposed  cause. 
The  tubes  and  tube-plates  are  to  be  cleaned  as  soon  as  possible 
after  steaming. 

It  is  essential  that  at  first  the  water  should  be  kept  for  a 
short  time  at  about  three  times  the  density  of  sea-water,  until 
the  thin  protective  scale  has  been  formed,  as  before  directed. 
After  this,  in  the  ordinary  working  of  the  boilers,  the  engineer 
officers  in  charge  of  machinery  are  to  use  their  discretion  as  to 
the  most  suitable  density  at  which  the  water  in  the  boilers 
should  be  kept  for  the  service  on  which  the  ship  is  employed. 
This  density,  which  is  in  no  case  to  exceed  three  times,  nor  be 
less  than  one  and  a  half  times  that  of  sea-water,  will  probably 
vary  to  some  extent,  on  different  stations  and  under  different 
conditions  of  working,  of  regular  service,  and  the  engineer  offi- 
cers will  be  guided  in  their  selection  of  the  working  density  by 
their  experience  of  the  economy  of  fuel  under  steam,  and  of 
the  state  of  the  boilers  after  steaming.  No  tallow  or  oil  of  ani- 
mal or  vegetable  origin  is  to  be  put  into  the  boilers  to  prevent 
priming,  nor  for  any  other  purpose  whatever. 

When  the  boilers  are  empty,  the  fires  are  not  to  be  kept 
laid  ;  the  boilers  are  to  be  kept  dry  and  warm  ;  all  accessible 
parts  are  to  be  frequently  examined  and  cleaned  ;  and  the 
lower  parts  are  to  be  coated  with  red  and  white  lead,  or  other 
protecting  substance.  Where  the  boilers  cannot  be  kept  thor- 


THE   MANAGEMENT  AND    CARE   OF  BOILERS. 


471 


oiigJily  dry  and  warm,  they  are;  at  the  discretion  of  the  engineer 
officer  in  charge,  to  be  kept  quite  full* 

The  boilers  should  not  be  exposed  to  sudden  changes  of 
temperature ;  the  steam  should  not  be  raised  rapidly ;  the 
smokebox  doors  should  not  be  opened  suddenly,  as  a  rush  of 
cold  air  through  the  tubes  affects  the  ends — and  the  tubes 
leak  ;  and  the  stop  and  safety  valves  should  be  opened  grad- 
ually. The  safety-valves  should  be  partially  raised  each  watch 
to  test  the  fittings,  and  the  smokebox  doors  should  not  be 
opened  except  when  absolutely  necessary.  The  blow-off  cocks 
are  to  be  kept  in  good  condition. 

The  spaces  at  the  backs  and  sides  of  the  boilers  are  at  all 
times  to  be  kept  clear ;  and  on  no  account  is  anything  combus- 
tible to  be  placed  on  the  top  of  the  boilers  or  in  contact  with 
them.  Every  care  is  to  be  taken  to  prevent  any  accumulation 
of  soot  or  coal-dust  between  the  uptake  and  casings  of  the  boil- 
ers, and,  when  necessary,  means  should  be  provided  for  exam- 
ining the  air-space  between  the  uptake  and  the  air-casing,  and 
every  possible  precaution  taken  to  prevent  the  clothing  of  the' 
boilers  being  set  on  fire. 

It  is  well  to  keep  a  log  in  the  boiler-room,  where  a  large 
"  plant"  is  operated,  and  the  record  so  kept  should  exhibit  all 
important  data  relating  to  its  operation.  The  following  is  a 
good  form  of  ruling  for  the  blanks  or  log-book  employed : 


BOILER   RECORD.— WEEK  ENDING. 


No.  of 
Boiler. 

Average 
Pressure. 

Hours 
Steaming. 

Coal, 
Tons. 

Ashes 
Removed 

Water 
Used. 

REMARKS. 

• 

Totals.. 

MEMORANDA.— 


*  A  small  quantity  of  washing  soda  or  other  alkali  may  be  introduced  with  ad- 
vantage. 


CHAPTER   XIII. 

THE   EFFICIENCIES   OF   STEAM-BOILERS. 

234.  Steam-boiler  Efficiency  is  not  'difficult  of  definition 
when  the  nature  of  the  quantity  to  be  measured  is  itself  first 
understood.  There  are,  however,  as  will  be  presently  seen, 
several  different  efficiencies  of  the  steam-boiler,  as  of  the  steam- 
engine  ;  and  it  is  important  that  each  be  distinctly  defined  be- 
fore a  study  of  either,  or  of  total  efficiency,  can  be  made.  In 
general,  it  may  be  said  that  efficiency  is  measured  by  the  ratio, 
in  common  or  similar  and  definitely  related  terms,  of  a  result 
produced  to  the  cost  of  its  production.  As,  in  the  study  of 
the  steam-engine,  either  efficiency  is  measured  by  the  ratio  of 
work  done  in  the  specified  manner  to  the  work  or  work-equiva- 
lent expended  in  doing  it ;  so,  in  the  case  of  the  steam-boiler, 
either  efficiency  is  measured  by  the  ratio  of  a  heat-effect,  or  its 
equivalent,  to  the  quantity  of  heat,  actual  or  latent,  paid  for 
its  accomplishment. 

In  some  cases  it  is  not  practicable  to  thus  establish  a  nu- 
merical value  of  an  efficiency ;  and  it  can  only  be  shown  that 
efficiency,  in  the  sense  of  quantity  of  result  compared  with 
magnitude  of  means  used,  is  increased  or  decreased  by  the  op- 
eration of  defined  phenomena,  or  by  conditions  which  can  be 
specified.  A  common  measure  cannot  always  be  found,  or  an 
exact  law  of  relation  established. 

Increasing  steam-pressure  gives  increasing  economy  up  to  a 
limit  somewhere  above  customary  pressures.  The  higher  the 
pressure  the  greater  the  economic  value  of  the  steam  in  a 
steam-engine,  but  on  the  other  hand  the  lower  the  efficiency 
of  the  boiler  ;  and  it  is  perfectly  possible  to  reach  a  point  at 
which  the  gain  on  the  first  score  is  more  than  counterbalanced 
by  the  loss  on  the  second.  Where  the  object  sought  is  simply 
heating-power,  the  advantage  lies,  on  the  whole,  on  the  side  of 
low  pressures. 


THE  EFFICIENCIES   OF  STEAM-BOILERS.  4/3 

235.  The  Measure  of  Efficiency  of  boilers  is  commonly  a 
ratio  of  heat  applied  to  a  defined  purpose  or  obtained  in  store, 
in  a  stated  form,  to  the  total  quantity  of  heat  from  which  it 
has  been  saved,  another  part  having   been  diverted    to  other 
purposes,  and,  for  the  use  considered,  wasted.     Thus,  a  given 
quantity  of  heat  being  stored  as  potential  energy  of  chemical 
action  in  fuel,  a  small  proportion  of  that  energy  is  received  at 
the  steam-engine  when  that  fuel  is  burned  under  a  steam-boiler  ; 
the  ratio  of  these  two  quantities — always  a  fraction  and  often 
small — is  the  total  efficiency  of  the  whole  apparatus  employed 
in  the  combustion  of  fuel,  the  transfer  of  heat-energy  to  the 
fluid  in  which  it  is  stored,  and  its  further  transfer  to  the  point 
at  which  it  is  usefully  applied  by  transformation  into  mechani- 
cal energy  and  work. 

236.  The    Efficiency   of  Combustion  thus  measures  the 
ratio  of  the  available  heat-energy  of  the  fuel  to  that  set  free  by 
its  union  with  oxygen,  and  is  less  than  unity  in  the  proportion 
in  which   the  combustible    portion   of   the    fuel    escapes  such 
chemical  change  or  is  imperfectly  burned,  as  when  a  part  of  the 
fuel  falls  into  the  ash-pit,  is  imbedded  in  clinker,  or   remains 
on  the  grate  when  the  fire  is  extinguished  ;  or  as  when  carbon 
is  only  oxidized   to   carbon  monoxide  instead   of  being  com- 
pletely burned    into  dioxide.     In  well-managed    furnaces   the 
value  of  this  efficiency  approaches  unity ;  it  ought  not  to  fall 
below  0.90,  probably,  in  any  ordinary  case. 

237.  The  Efficiency  of  Transfer  of  Heat  similarly  meas- 
ures the  ratio  of  heat  received  from  the  furnace  by  the  boiler 
to  that  produced  by  combustion.     That  not  transferred  to  the 
boiler  is  either  sent  up   the  chimney,  where  it  is,  in  a  certain 
degree,  useful  in  producing  draught,  or  it  is  lost  by  conduction 
and  radiation  to  surrounding  bodies.     In  good  examples,  the 
value  of  this  ratio  exceeds  0.75,  and  it  should  not  usually  fall 
under  fifty  or  sixty  per  cent.     Its  best  value  depends  on  con* 
siderations,  however,  to   be  hereafter  stated,  and   it  is  not  al- 
ways desirable  that  it  should  have  the  highest  value  possible, 
or  approximate  unity. 

238.  The  Net  Efficiency  of  Boiler  is  the  continued  prod- 
uct of  all  efficiencies  of   the  several  operations  constituting  the 


474  THE   STEAM-BOILER. 

process  of  production  and  supply  of  steam  ;  and  it  can  only  be 
exactly  known  by  direct  experimental  determination,  either  as 
a  whole,  or  in  detail,  by  the  ascertainment  of  the  values  of 
each  of  its  factors.  It  is  this  quantity  with  which 'the  engineer 
and  the  proprietor  are  principally  concerned,  and  the  study  of 
the  elementary  efficiencies  is  mainly  useful  in  revealing  the 
causes  and  the  extent  of  wastes  in  the  several  steps  of  the 
whole  process. 

239.  The  Finance  of  Efficiency  is  a  more  important  mat- 
ter, if  possible,  than  the  theory  of  either  or  all  the  efficiencies 
already  defined.     It   is  obvious  that,  in  any  case  in  which  steam 
is  demanded  at  a  given  pressure  and  in  stated  quantity,  it  may 
be   obtained  either  expensively  by  using   ill-chosen  types,  con- 
struction, and  proportion  of  boiler,  and    operating   under   un- 
fortunate conditions,  or  economically  by  an  opposite  method. 
In  general,  the  larger  the   boiler  the  less   the  cost  of  steam  in 
fuel  and  operating  expenses ;  the  smaller  the  boiler  the  heavier 
the  coal  bills  and   related  accounts.     On  the  other  hand,  the 
larger  boiler  is  of  great  first  cost,  expensive  in  its  interest,  in- 
surance, and  perhaps  maintenance,  accounts ;  while  the  oppo- 
site is  true  of  the  smaller  boiler.     It  is  equally  evident  that  a 
boiler  may  be  too  large  and  costly  for  real  and  ultimate  financial 
economy  ;  or  it  may  be  too  small  and  too  wasteful  of  fuel  to  give 
best  results  as  read  on  the  final  balance-sheet,  at  the  end  of  its 
period  of  service.    There  must  in  every  case  be  some  proportion 
of  size  and  cost  to  quantity  of  steam  demanded  which  shall,  on 
the  whole,  prove   in  the  end   a  financial  success,  and  give  the 
work  required  of  it  at  the  least  total  cost. 

240.  Commercial  Efficiency  must  thus  be  added  as  the 
final  and  most  important  of  all  efficiencies,  as  judged  from  the 
standpoint  of  the  proprietor,  and  as  measuring  also  the  success 
of  the  designer  of  the  steam-generating  apparatus  ;  and  the  fol- 
lowing definitions  and  principles  may  be  admitted  as  a  basis 
for  the   mathematical  theory   of   the    finance   of   steam-boiler 
operation : 

In  the  design  and  construction  of  a  steam-boiler,  and  in  its 
operation,  problems  arise  which  must  be  solved  by  the  mechan- 
ical engineer  in  their  natural  order  before  he  can  say  with 


THE   EFFICIENCIES   OF  STEAM-BOILERS,  4?$ 

confidence  that  the  best  interests  of  the  purchaser  or  proprietor 
of  the  apparatus  are  fully  met  in  its  construction  and  manage- 
ment. Such  are  the  following : 

(1)  TJie  "Efficiency  of  the  Steam-boiler'  is  the  ratio  of  the 
total  quantity  of  heat  utilized  in  the  production  of  steam   to 
that   set  free   in  the   combustion   of  the   fuel.     It   has  as  the 
maximum  limit  unity,  and  is  a  function  of  area  of  heating-sur- 
face, and   of  factors  dependent  upon  the  character  of  the  fuel 
and  its  combustion,  and  upon  the  design  of  the  boiler. 

(2)  The  "  Commercial  Efficiency'  or  the  "  Efficiency  of  Capi- 
tal" employed  in  the  maintenance  of  steam-generating  appa- 
ratus of  a  given  power  is  measured   by  the  ratio  of  quantity  of 
steam  produced  to  the  total  cost  of  its  continuous  production, 
i.e.,  by  the  reciprocal  of  the  total  cost  of  steam  per  pound  or  per 
cubic  foot  at  the  required  pressure.  This  efficiency  is  a  maximum 
when  that  cost,  is  a  minimum. 

(3)  The  "Efficiency  of  a  Given  Boiler  Plant"  as  the  Author 
has  called  it,  or  the   commercial  efficiency  of    a    steam-boiler 
already  in  place  and  in  operation,  is  still  another  quantity.     It 
is   a  maximum  when  the  work  done  by  the  boiler  can  be  in- 
creased   beyond    that  for  which   it    was    proportioned — if  de- 
signed originally  to  give  maximum  efficiency  of  capital  at  a  pre- 
arranged power,  as  above — until  the  amount  of  steam  made  by 
that  boiler  per  dollar  of  working  expense  is  made  a  maximum. 

These  three  efficiencies  differ  essentially  in  their  character, 
and  are  determined  by  different  processes.  In  the  first  case,  the 
engineer  designing  a  boiler  finds  himself  called  upon  to  deter- 
mine what  is  the  maximum  efficiency  that  it  will  be  economical, 
or  otherwise  advisable,  to  endeavor  to  secure,  and  then  cal- 
culates the  proportions  necessary  to  secure  that  efficiency. 
Or,  knowing  the  proportions  of  any  boiler  already  designed  and 
built,  he  may  be  required  to  calculate  its  probable  efficiency 
and  the  quantity  of  fuel  required  to  make  a  certain  quantity  of 
steam,  i.e.,  to  estimate  the  quantity  of  steam  which  will  be 
generated  per  pound  of  coal  burned. 

In  the  second  case,  the  designing  engineer  calculates  the 
proportions  of  heating-surface  to  grate-surface  or  to  fuel 
burned,  where  the  quantity  of  steam  required  is  known,  and  the 


4/6  THE   STEAM-BOILER. 

conditions  determining  costs,  which  shall  give  that  quantity  of 
steam  at  least  total  running  expense.  The  investigation  de- 
termines how  large  a  boiler  or  what  extent  of  heating-surface 
will,  all  things  considered,  pay  best. 

In  the  third  case,  the  boiler  is  in  place  and  in  operation,  and 
it  is  found  that  it  is  advisable  to  ascertain  what  quantity  of 
steam  is  made  when  the  cost  of  that  steam,  per  unit  of  weight 
or  of  volume,  becomes  a  minimum. 

In  the  first  two  cases,  the  variable  element  is  usually  the  area 
of  heating-surface  per  pound  of  fuel  burned  in  the  unit  of  time ; 
in  the  last,  the  variable  may  be  either  the  quantity  of  fuel 
burned  or  of  steam  made. 

(4)  To  ^vhat  Capacity  may  any  Given  Boiler  be  forced  with- 
out exceeding  that  Cost  of  Steam  at  which  a  Paying  Profit  is 
given  ?  is  another  problem  in  steam-boiler  efficiency,  and  one 
which  is  of  more  frequent  occurrence  and  is  usually  more  im- 
portant than  the  preceding. 

The  economical  maximum  of  steam-production  is  evidently 
determined  by  the  money  value,  to  the  producer,  of  the  steam 
made. 

241.  Efficiency  of  the  Steam  Boiler. — This  case  has  been 
studied  by  Rankine,  who  deduces  a  very  simple  and  handy 
formula  for  the  efficiency  of  a  boiler  of  known  proportions, 
using  a  fuel  of  known  calorific  value. 

Taking  the  rate  of  conduction  of  heating-surfaces  as  varying 
as  the  square  of  the  difference  of  temperatures  of  the  gas  and 
of  the  water  on  opposite  sides  of  the  sheet,  the  formula 


is  readily  deduced,  in  which  E  is  the  efficiency,  a  a  constant,  cr 
the  specific  heat  of  the  furnace-gases,  and  W  their  weight ; 
while  H  is  the  total  heat  expended  and  5  the  heating-surface. 
This  expression  is  further  transformed  into 

' 


THE  EFFICIENCIES  OF  STEAM-BOILERS.  477 

in  which  E  is  the  theoretical  evaporative  power  of  the  fuel  per 
pound,  El  the  probable  actual  evaporation  in  a  boiler  in  which 
F  is  the  weight  of  fuel  burned  on  the  unit  of  area  of  grate,  and 
5  is  the  area  of  heating-surface  per  unit  of  the  same  area. 

A  and  B  are  here  coefficients,  having  values  respectively  of 
0.3  to  0.5  and  0.9  to  I  for  bituminous  coals,  according  to  Ran- 
kine,  and  from  0.3  to  0.5  and  from  0.8  to  0.9  with  anthracite 
coal,  as  determined  by  experiments  made  by  the  Author.  The 
lowest  and  best  values  of  A  are  obtained  when  using  a  minimum 
needed  air-supply,  and  the  value  of  that  coefficient  is  seen,  by 
comparing  the  two  equations  just  given,  to  vary  as  the  square 
of  the  quantity  of  air  supplied  to  the  fuel.  The  value  of  B  is 
dependent  upon  the  character  of  the  boiler,  being  greater  as 
the  design  and  construction  are  improved. 

The  following  are  illustrations  of  the  results  thus  obtained : 
EFFICIENCY  OF  STEAM-BOILERS. 

I.  II.  III.  IV. 

p 
—    ,4  =  0.5;  .5=1.     .4  =  0. 3;  ,5=1.     ^=0.5;^  =  !.     A=   0.3;  B=i. 

0.17  0.92  0.95  0.83  0.86 

0.33  0.87  0.91  0.78  0.82 

0.40  0.83  0.89  0.75  0.80 

0.50  0.80  0.87  0.72  0.78 

0.67  0.75  0.83  0.68  0.75 

242.  Commercial  Efficiency  of  the  Boiler. — The  expenses 
of  operating  a  steam-boiler  may  be  classed  under  three  heads : 

(1)  Those  costs  of  boiler  and  its  maintenance  which  are  de- 
pendent upon  the  size  and  the  character  of  the  boiler  itself  and 
its  attachments,  such  as  interest  on  cost  of  boiler  and  setting, 
rent  of  building,  and  other  items  on  construction  account,  such 
as  taxes,  insurance,  repairs  and  depreciation,  etc.,  etc. 

(2)  Those  costs  of  operation  which  are  dependent  upon  the 
quantity  of  steam  made  and  of  fuel  consumed,  such  as  market 
price  of  fuel,  cost  of  transportation,  storage  (an  important  item 
on  shipboard  especially),  and  of  feeding  into  the  furnace,  cost 
of  feed-water  and  its  introduction  into  the  boiler,  and  often  a 
certain  part  of  other  costs  of  attendance  and  supply. 

(3)  In  addition  to  these  variable  expenses  are  often,  perhaps 
usually,  to  be  counted  certain  constant  expenses  which  are  un- 


478  THE   STEAM-BOILER. 

affected  by  any  change  of  proportions  of  boiler  likely  to  be 
made  in  the  assumed  case,  such  as  nearly  all,  or  frequently  quite 
all,  the  costs  of  attendance. 

A  given  amount  of  steam  being  demanded,  it  may  be  ob- 
tained either  from  a  boiler  so  small  as  to  use  fuel  extravagantly, 
or  from  a  large  boiler  using  fuel  economically.  In  each  case 
arising  in  practice,  there  will  be  found  a  certain  easily  deter- 
mined proportion  of  heating-surface  to  grate-surface,  and  a 
definite  size  of  boiler  which  will,  on  the  whole,  supply  the  de- 
sired quantity  of  steam  most  economically.  Thus  : 

Let  the  total  cost  of  fuel  per  annum  and  per  pound  burned 
per  hour  on  the  square  foot  of  grate  or  on  the  square  metre  be 
called  C.  Let  the  total  cost  per  annum  of  boiler,  per  square 
foot  or  per  square  metre  of  heating-surface,  be  called  D,  and  let 

j.  —  R.     In  the  first  item  is  included  Class  i,  and  in  the  second 

Class  2. 

Then  the  cost  of  boiler  maintenance  per  annum  is  DSG, 
where  5  is  the  area  of  heating-surface  per  unit  of  area  of  grate 
and  G  is  the  area  of  grate.  The  cost  of  fuel,  etc.,  per  annum, 
as  per  Class  2,  is  CFG,  if  F  is  the  weight  of  fuel  burned  per 
unit  of  area  of  grate. 

The  total  of  costs  variable  with  change  of  proportion  of 
boiler  is 

P=DSG+CFG. 

The  profitable  work  of  the  boiler  is  measured  by  the  quantity, 
by  weight,  of  steam  made,  FG£1=  W\  El  being  the  evapora- 
tion of  water  per  unit  of  weight  of  fuel. 

The  ratio  of  cost  to  work  done  is 

/>  _  DGS  +  CFG  _  CF+DS 
"  W~~          FGE,  Ef 

This  quantity  being  made  a  minimum  by  variation  of  the 
area  S,  the  most  economical  boiler  is  obtained. 

But  El  is  a  function  of  S,  and,  taking  the  value  of  El  from 
the  equation 


'+-5- 


THE   EFFICIENCIES   OF  STEAM-BOILERS.  479 


we  obtain 


ACF^G 


BEFG 


which  is  a  minimum  when 


BEFG 


BEF 


-v  =  VAR. 


In  illustration :  Let  a  boiler,  set  in  place,  complete  with  all 
its  appurtenances  and  in  running  order,  cost  $3  per  square  foot 
of  heating-surface,  and  the  annual  charges  on  all  accounts  en- 
tered in  Class  I,  above,  be  20  per  cent  on  this  cost,  the  annual 
charge  becomes  DS  =  $0.60  X  5  per  square  foot  of  grate,  i.e., 
D  —  $0.60.  Let  the  cost  of  operation,  as  for  Class  2,  amount 
to  $15  per  annum  per  pound  of  fuel  burned  per  hour  on  the 

C 
square  foot  of   grate;  then  CF=$i$  X  F\    ^=$15  ;  -^  =  R 

=  25. 

Assume  F  =  10  pounds  of  fuel  per  hour  per  square  foot  of 
grate,  A  =0.5. 

For  this  case,  then,  the  boiler  should  have  per  square  foot 
of  grate, 

S,=FV~AR=  10  X  (0.5  X25)£  =  35; 

35  square  feet  of  heating-surface. 

Similarly  we  get  the  following  values : 

COMMERCIAL   EFFICIENCY  OF   BOILERS. 

Ratio  of  Areas  of  Heating  and  Grate  Surfaces. 

Values  of  S. 


F 

6 

10 

12 

T5 

20 

3° 

40 

5° 

R 
25 
16 

9 

4 

21 

17 
12 

8 

35 
28 

21 
14 

42 

34 
24 
16 

52 
42 
32 
21 

70 
56 
42 

28 

105 

84 

63 
42 

140 
112 

84 
56 

175 
140 
105 
70 

480  THE   STEAM-BOILER. 

These  values  are  20  or  25  per  cent  lower  for  forced  draught. 

Where  the  boiler  is  worked  almost  continuously,  as  in  flour- 
mills  and  some  other  establishments  kept  in  operation  night 
and  day  throughout  the  year,  the  higher  values  will  be  found 
correct  ;  when  the  boiler  is  worked  discontinuously  or,  as  in 
steam  fire-engines  and  some  classes  of  steam-vessels,  a  com- 
paratively small  proportion  of  the  annual  working  time  of  the 
establishment  or  whole  plant,  the  values  of  S1  become  very 
small. 

It  is  seen  that  the  best  area  of  heating-surface  will  vary 
nearly  as  the  square  root  of  the  total  working  time  per  annum. 
Boilers  worked  continuously,  worked  twelve  hours  out  of  the 
twenty-four,  and  eight  hours  in  the  day,  will  require,  respective- 
ly, values  of  5  having  the  proportion  I,  0.7,  and  0.6  nearly. 

W 
The  total  required  area  of  grate  is  -=--=,=.  G\  the  total  area 


,  W(S1+AF) 

of  heating-surface  is  -j=^-  =  S.G  —  : 


The  following  are  examples,  in  greater  detail,  of  the  appli- 
cation of  the  above  : 
EXPENSE  ON  BOILER  ACCOUNT  AND  MAXIMUM  COMMERCIAL  EFFICIENCY. 

CASES.                                                                           STATIONARY.  MARINE. 

I.  II.  III.         IV. 

Class  i  (Z>)                                          Cornish.  Tubular.  Tubular.  Tubular. 

Total  annual  cost  of  boiler  per  unit  of  5..  ...     $1.50  $2.00  $3.00      $2.00 

Interest  ......................  ;  ............         .09  .12  .15           .12 

Repairs  and  depreciation  ....................  15  .20  .45           .30 

Rent,  insurance,  and  miscellaneous  .....  .....         .10  .07  i.oo          .20 

Total  value  of  D  ...................  34  .38  1.60           .62 

Class  2  (C). 
Fuel  (@  $5  for  I.,  II.,  IV.;  $4  for  III.)  per  unit 

Of  F  .................................          7.50  7.20         12.00  2.00 

Transportation  and  storage  .................        r.oo         i.oo       10.00         i.oo 

Attendance  (variable  cost)  ..................       o.oo        0.50        0.50        o.oo 

Total  .......  .  .....................       8.50         9.00       22.50         3.00- 

Value  oi—=R  ..................     25  23  14  5 

Value  of  A  ......................       0.5  0.3  0.3         0.5 

Value  of    tf~AR  ..................       3.5  2.7  2.0         1.6 

Value  of  F  ......................        8  10  16  20 

Value  of  t^AR  —  Si  ..............      28  27  32  32 


THE  EFFICIENCIES  OF  STEAM-BOILERS.  481 

R  varies  in  magnitude  very  greatly  in  practice,  falling  as  low 
as  4  and  rising  as  high  as  50  with  varying  cost  of  fuel  and 
length  of  working  time. 

The  engineer  thus  solves  this  important  problem  in  boiler- 
design  which  may  be  thus  enunciated  :  To  determine  the  com- 
mercial efficiency  of  a  steam-boiler  doing  a  fixed  amount  of 
work  ;  or,  given  all  variable  expenses  of  boiler  installation, 
maintenance,  and  operation,  to  determine  what  proportion  of 
heating-surface  to  grate-surface,  or  to  fuel  burned,  will  give  the 
required  amount  of  power  at  least  total  cost. 

243.  Commercial  Efficiency  of  a  Fixed  Plant.—  A 
second  commercial  problem  may  sometimes  be  presented  to  the 
engineer  :  A  steam-boiler  is  in  place  and  in  operation  ;  all  con- 
stant expenses  are  known  and  all  variable  costs  of  mainten- 
ance and  operation  are  determinable.  The  question  arises, 
or  may  arise  whenever  additional  steam  may  be  usefully 
employed  :  How  much  work  can  be  obtained  from  the  ap- 
paratus when  driven  to  such  an  extent  as  to  yield  the  maximum 
amount  of  steam  per  dollar  of  total  cost  of  operation  ?  The 
independent  variable  is  now  the  quantity  of  fuel  burned  in  the 
boiler,  and  this  is,  in  the  established  equation,  represented  by 
F,  the  fuel  burned  per  unit  of  area  of  grate.  This  problem  is 
thus  stated  : 

Given  :  All  expenses,  constant  and  variable,  the  method 
of  variation  of  the  latter,  and  the  proportions  of  the  boiler 
being  given,  to  determine  that  rate  of  combustion  which  will 
make  the  commercial  efficiency  of  the  given  plant  a  maximum. 

For  this  case  let  K  represent  that  total  annual  expense  of 
working  which  is  independent  of  Classes  I  and  2  and  which  falls. 

7f 

into  Class  3,  and  let  k  =  -^. 

Let  all  other  symbols  stand  as  before. 

Then  the  total  cost  of  maintenance  and  operation  will  be 


while  the  work  done  will  be,  as  before, 


31 


THE   STEAM-BOILER. 

The  quantity  to  be  made  a  minimum  is,  for  the  present  case, 
the  quotient  of  P  by  W, 

_P 

~  VV : 

F  being  taken  as  the  independent  variable. 

This  becomes  a  minimum  when  we  substitute  for  El  its  value 

BE 

£l  =  —  ,  and  make  the  first  derivative  equal  zero. 

i+-s-  •  ; 

Then  we  find 


When,  in  this  expression  for  the  value  of  /%  giving  maxi- 
mum weight  of  steam  for  the  dollar  expended,  we  make  k  =  o, 
the  expression  maybe  reduced,  as  obviously  should  be  possible, 
to  the  form  shown  already  to  be  that  giving  the  solution  of 
the  first  problem  : 


The  following  cases  illustrate  this  problem  : 

EXPENSES  OF  BOILER  AND  MAXIMUM  ECONOMY  OF  PLANT. 

CASES.                                                  STATIONARY.  MARINE. 

I.              II.  III.          IV. 

Cost  of  maintenance  :  D  .....  ..........  ,.,     $0.34        $0.58  $0.88         $0.62 

Cost  of  operation  :          C.  .......    .........        8.20-         9.00  14.50           3.00 

Cost  of  operation  :         K.  .................     30.00         25.00  10.50         10.00 

For  maximum  fuel  and  work  :  F\  ..........     16  13  17  21 

For  maximum  efficiency,  as  before  :  F  .....       8  10  16  20 

Case  No.  I  is  that  of  a  Cornish  boiler,  No.  2  that  of  a  mul- 
titubular  stationary  boiler,  No.  3  that  of  a  sea-going  steamer, 
and  No.  4  that  of  a  yacht. 

It  is  seen  that  in  all  cases  the  weight  of  steam  delivered  from 
the  boiler  and  the  quantity  of  fuel  burned  at  maximum  com- 
mercial efficiency,  for  the  case  assumed,  are  less  than  where  the 
boiler  —  once  set  and  still  capable  of  being  forced  to  deliver 


THE  EFFICIENCIES   OF  STEAM-BOILERS.  483 

more  steam  than  originally  proposed  and  calculated  upon — is 
worked  up  to  a  maximum  delivery  per  dollar  of  total  expense. 

"  Maximum  commercial  efficiency  of  boiler"  and  "Maxi- 
mum efficiency  of  a  given  plant  "  are  therefore  by  no  means 
identical  conditions  ;  and  it  will  usually  be  found  that  when  this 
maximum  work  can  be  put  on  the  boiler,  it  might  be  done  still 
more  economically  by  a  boiler  specially  designed,  as  in  the  first 
problem,  to  do  the  increased  quantity  of  work :  the  conclusion 
from  this  fact  being  simply  that  economy  dictates  that  as  much 
steam-power  as  possible  should  be  grouped  into  a  single  plant 
in  order  to  diminish  the  proportional  cost  of  the  constant  part 
of  running  expenses,  i.e.,  otherwise  stated,  there  being  given  a 
certain  necessary  expenditure,  invariable  within  certain  limits 
with  variation  of  size  of  boiler  or  of  quantity  of  steam  made, 
the  larger  the  amount  of  work  done  without  increasing  this 
constant  expense,  the  cheaper  will  the  steam  be  made. 

The  larger  the  plant  supervised  by  the  engineer  the  less  the 
total  cost  per  pound  of  steam  made,  other  conditions  of  econ- 
omy being  unchanged. 


CHAPTER   XIV. 

STEAM-BOILER    TRIALS. 

244.  The  Object  of  a  Trial  of  a  Steam-boiler  is  to  de- 
termine what  is  the  quantity  of  steam  that  a  boiler  can  supply 
under  definitely  prescribed  conditions ;  what  is  the  quality,  as 
to  moisture  or  dryness,  of  that  steam  ;  what  is  the  amount  of 
fuel  demanded  to  produce  that  steam  ;  what  the  character  of 
the  combustion,  and  the  actual  conditions  of  operation  of  the 
boiler  when  at  wrork.  The  conditions  prescribed  for  one  trial 
may  differ  greatly  from  those  of  another  trial,  and  such  differ- 
ences are  often  the  essential  matters  to  be  studied.  In  any 
case  it  is  assumed  that  the  conditions  under  which  the  boiler  is 
to  be  worked  are  to  be  definitely  stated,  and  the  engineer  con- 
ducting the  experiments  is  expected  to  ascertain  all  the  facts 
which  go  to  determine  the  performance  of  the  boiler,  and  to 
state  them  with  accuracy,  conciseness,  and  completeness. 

In  the  attempt  to  ascertain  those  facts  the  engineer  meets 
with  some  difficulties,  and  finds  it  necessary  to  exercise  the 
utmost  care  and  skill.  In  conducting  a  steam-boiler  trial  the 
weight  of  the  water  supplied  to  the  boiler  must  be  determined  ; 
the  weight  of  the  fuel  consumed  must  be  obtained  ;  the  state 
of  the  steam  made  must  be  determined  ;  and  these  quantities 
must  all  be  noted  at  frequent  intervals.  It  is  also  necessary  to 
know  whether  the  combustion  is  perfect  or  imperfect,  and  to 
what  extent  the  conditions  and  facts  noted  are  due  to  the 
boiler,  and  what  to  external  conditions. 

It  has  now  come  to  be  considered  that  the  determination  of 
power  and  economy  of  a  steam-boiler  demands  all  the  care,  skill, 
and  perfection  of  method  and  of  apparatus  of  any  purely  scien- 
tific investigation.  It  is  essential  that  all  work  of  this  kind  shall 
be  done  in  substantially  the  same  way,  in  order  that  compari- 
sons may  be  made. 


STEAM-BOILER    TRIALS.  485 

245.  Tests  of  Value  of  Fuel  are  sometimes  the  sole  object 
of  a  trial  of  a  steam-boiler,  the  intent  being  to  ascertain  by 
actual  experiment  what  quantity  of  water  a  fuel  of  unknown 
quality  can  evaporate  in  a  boiler  of  which  the  general  efficiency 
is  fairly  well  established.  In  such  cases  the  fuel  is  employed 
in  the  usual  manner  and  the  results  compared  with  those  ob- 
tained with  fuels  of  known  excellence.  Thus,  in  a  good  type  of 
boiler,  having  a  good  proportion  of  area  of  heating-surface  to 
weight  of  fuel  burned  per  hour,  it  may  be  found  that  a  fuel  of 
established  reputation  for  uniform  excellence  will  evaporate  ten 
times  its  own  weight  of  water  "  from  and  at "  the  boiling-point. 
The  trial  of  a  fuel  of  unknown  quality  may  prove  that  this 
boiler  will,  under  precisely  similar  conditions,  evaporate  an 
equal  amount  of  water  into  steam,  and  yet  the  market  price  of 
the  fuel  may  be  considerably  less  than  that  of  the  other. 
The  immediate  result  would  be  the  substitution  of  the  second 
for  the  first,  should  no  counterbalancing  disadvantages  exist. 
In  such  cases  the  method  of  conducting  the  experiment  is 
precisely  the  same  as  where  the  efficiency  of  the  boiler  is  de- 
termined ;  but  the  object  sought  is  quite  a  different  one.  This 
also  commonly  compels  at  least  two  trials,  the  one  of  the 
old  and  standard,  the  other  of  the  new  and  uncertain  fuel,  and 
a  comparison  of  boiler-efficiency  as  found  in  the  two  trials. 

246.  The  Determination  of  the  Value  of  a  steam-boiler 
involves  the  measurement  of  its  efficiency,  independently  of  the 
nature  of  the  fuel,  and  it  is  thus   important   that  a  standard 
system  of  measuring  the  effectiveness  of  the   fuel   should  be 
settled  upon,  or  that  all  variations  of  such  effectiveness  should 
be  eliminated.     The  latter  is  commonly  the  course  taken  ;  and 
the  determination  of  the  efficiency  of  the  boiler  is  based  upon 
the  measurement  of  the    evaporation  of  water,   under  stated 
standard    conditions,   per  unit  weight  of  the  combustible  and 
burned  portion  of  the  fuel  supplied  during  the  trial. 

But  the  power  of  the  boiler  is  as  important  an  element  of 
its  value  as  its  efficiency,  and  a  complete  trial  includes,  usually, 
measurements  of  efficiency  at  both  the  rated  and  the  maximum 
working  power  of  the  boiler  as  operated  for  its  special  purpose. 

247.  The    Evaporative    Power  of  Fuels   depends   upon 


486  THE   STEAM-BOILER. 

not  only  their  chemical  composition  as  fuels,  but  also  to  an 
important  extent  upon  their  structure  and  their  physical  con- 
dition in  every  aspect ;  on  their  greater  or  less  purity,  and  the 
admixture  of  earths,  moisture,  or  other  foreign  matters ;  the 
fitness  of  the  furnace  for  their  utilization ;  the  air-supply ;  its 
quantity,  temperature,  and  humidity ;  the  proximity  of  chilling 
surfaces ;  the  extent  of  the  combustion-chamber  in  which  the 
gases  rising  from  the  bed  of  coal  or  other  combustible  may  be 
more  or  less  completely  consumed  ;  and  many  other  minor  con- 
ditions, all  of  which  tell,  in  a  more  or  less  important  degree, 
upon  their  value  and  the  efficiency  of  the  system  of  heat- 
generation. 

248.  Analyses  of  Fuels  are  sometimes  made,  either  as  a 
check  upon  the  results  of  the  trial  or  in  substitution  for  it. 
Should  analysis  show  that  a  given  fuel  is  rich  in  heat-producing 
elements,  while  trial  fails  to  give  the  results  that  should  have 
been  obtained,  and  such  as  the  use  of  other  fuels  in  the  same 
boilers  indicates  to  be  possible,  it  will  at  once  appear  that  the  fuel 
demands  peculiar  treatment,  or  some  other  arrangement  of 
furnace.  Should  doubt  exist  which  of  a  number  of  fuels  of  the 
same  class  is  best,  chemical  analysis  may  give  a  quicker  and 
cheaper  answer  to  the  question  than  a  formal  trial.  It  rarely 
happens,  however,  that  any  system  is  as  satisfactory,  in  the  end, 
as  actual  trial  extending  over  so  long  a  period  as  to  eliminate 
uncertainties. 

Methods  of  analysis  differ  somewhat.  The  following  is  a 
standard  method  of  general  treatment  as  prescribed  by  the 
Union  of  Engineers  of  Germany  :* 

In  order  to  take  a  sample  of  the  fuel,  a  shovelful  from 
each  barrow  or  wagon  will  be  thrown  into  a  box  with  a  cover. 
The  coal  will  be  mixed  up  and  spread  in  the  form  of  a  square 
upon  a  level  floor,  and  then  divided  by  two  diagonals  into  four 
parts.  Of  these,  two  opposite  parts  will  be  taken  away,  the 
other  two  will  be  broken  up  small  and  mixed  together.  Another 
shovelful  will  then  be  thrown  in,  and  the  method  continued 
until  about  10  kilogrammes  are  in  the  box.  This  will  then  be 

*  American  Engineer,  August,  1883. 


STEAM-BOILER    TRIALS.  487 

closed  and  reserved  for  chemical  analysis.  For  accurate  ex- 
periments the  halves  which  have  been  taken  away  should  also 
be  analyzed. 

To  determine  the  moisture  in  the  coal,  about  10  grammes 
from  the  above-named  sample  is  to  be  heated  for  two  hours  to 
105°  or  110°  C.  The  loss  in  weight  shows  the  moisture  in  the 
coal.  Coal  which  happens  to  have  been  wetted  by  rain  or 
otherwise  should  not  be  used.  The  test  should  be  applied  to 
coal  in  the  average  state  of  moisture  at  which  it  is  delivered 
from  the  pit  mouth,  and  this  state  should,  if  necessary,  be 
determined  beforehand.  The  remainder  of  the  sample,  pow- 
dered and  mixed  thoroughly,  serves  to  determine  the  ash,  the 
carbon,  the  hydrogen,  the  nitrogen,  and  the  sulphur.  The 
heating-value  of  the  coal  is  determined  as  follows  :  Suppose 
that  it  is  found  to  contain  c  per  cent  of  carbon,  h  per  cent  of 
hydrogen,  s  per  cent  of  sulphur,  o  per  cent  of  oxygen,  and  w 
per  cent  of  water,  then  the  theoretical  heating-value  is  given 
by  the  formula  of  Dulong  as  follows  : 

(a).     Referred  to  Water  at  o°  Cent. 

8100^   +    34320  (/i  —  gj    +250*. 

(b\     Referred  to  Water  at  100°  Cent. 

SIQOC+  34200  \k  —  ?j    +    2$oos  —  636.5  (g/i  +  w.) 

To  determine  the  quantity  of  air  required  for  burning  coal 
we  have  the  following:  One  kilogramme  of  coal  requires  to 
burn  it, 

2.667^   +    S/i  +  s  —  o 

"  cu>  metres  of  oxygen  ;  or> 


loo  x  1.43 

2.667*:   -f    8^  +  s  —  o 

--  —  --  cu.  metres  of  air  containing  21  per  ct. 

of  oxygen. 

The  analyses  should  be  made  with  care,  by  a  skilled  and 
experienced  chemist,  if  any  important  question  is  to  be  settled. 

249.  Economy  of  Fuel  is  nearly  synonymous  with  effi- 
ciency of  boiler,  as  a  matter  of  engineering  simply  ;  but  when 
the  finance  of  the  case  is  studied,  it  is  often  found,  from  that 


THE   STEAM-BOILER. 

point  of  view,  a  very  different  mattter.  It  is  perfectly  possible 
to  adopt  so  great  a  proportion  of  heating-surface,  so  large  a 
boiler,  that  the  gain  in  fuel  saved,  as  compared  with  boilers  of 
similar  type  and  usual  proportions,  may  be  more  than  offset 
by  the  increased  charges  on  account  of  enlargement  of  boiler. 
The  efficiency  of  boiler,  in  the  ordinary  sense  in  which  that 
term  is  used,  is,  however,  a  measure  of  economy.  The  varia- 
tion of  efficiency  and  of  economy  in  fuel  consumption  is  a  func- 
tion of  the  proportion  of  area  and  of  heating-surface  to  fuel 
burned,  and  the  object  of  a  boiler-trial  is  to  ascertain  these  rela- 
tions with  precision.  An  understanding  should  be  had  before 
the  trial  in  regard  to  the  kind  of  fuel  to  be  used  ;  where  no  reason 
of  controlling  importance  exists  to  the  contrary,  the  best  obtain- 
able coal  should  be  selected,  for  the  reason  that  a  boiler  can  be 
better  judged,  and  the  results  of  its  trial  may  be  more  satisfac- 
torily compared  with  similar  trials  of  other  boilers,  when  the 
very  best  work  of  which  it  is  capable  is  done  by  it.  The 
differences  between  separate  lots  of  the  best  coals  are  less 
than  the  differences  between  separate  lots  of  inferior  fuels, 
and  the  comparison  is  thus  less  difficult  where  the  former  are 
used. 

The  results  of  a  boiler-trial  at  Cassel  are  reported  to  have 
given  the  following  distribution  of  heat  :* 

B.  T.  U.  per  cent. 

Heat  of  I  Ib.  coal  utilized 11,498.4  80.34 

Carried  off  by  gases 1.031.4  7.21 

"    "  brickwork 286.2  2.00 

"    "  ashes 2340  1.63 

"         "     "   radiation,  etc 1,261.8  8.82 

14,311.8     100.00 
The  coal  contained : 

C 82.51  percent. 

H 4-73    "      " 

0 4.68"      " 

H20 1.38    "      " 

Ash  and  Waste 6.70    "      " 


100.00 


*  Abstracts  of  Papers,  XC.,  1887,  p.  70,  Inst.  C.  E. 


STEAM-BOILER    TRIALS,  489 

The  data  of  the  trial  were : 

Steam  pressure  (atmos.) 6.36 

Water  evap.  per  hr.,  Ibs 4,501.79 

"         "        "    sq.  ft.  H.  S.  per  hr.,  Ibs 2.99 

"         "        "    Ib.  coal,  Ibs 10.50 

Temp,  feed-water  in  tank  (Fahr.) 64°. 4 

"         "         "      from  heater 115°. 52 

"      air  in  boiler-house 69°. 8 

"      gas  leaving  flues 345°. 2 

Ratio  air  to  theoretical  quantity 1.31 

Coal  per  sq.  ft.  G.  S.  per  hr.,  Ibs 14-67 

"      "    "    "  H.  S.    "     "      " 0.297 

250.  The  Relative  Values  of  Boilers  depend  not  only  on 
their  efficiencies,  but  also  on  their  capacities  for  furnishing  steam, 
and  on  various  other  qualities  and  attributes :  as  their  greater 
or  less  complication  in  structure  ;  their  safety  and  durability  ; 
their  volume,  weight,  and  cost.     The   boiler-trial    only   settles 
questions  relating  to  their  efficiency  and  capacity,  and  their  real 
relations  of  value,  only  just  so  far  as  those  elements  enter  the 
problem.     These  are  usually,  however,   the    main  factors,  and 
their  measurement  by  a  test-trial  gives  the  means  of  deciding, 
in  nearly  all  cases,  every  question  likely  to  present  itself  in  the 
use  of  the  apparatus. 

251.  Variations  of   Efficiency   occur   with   variations    in 
grate-area,    in    rate    of   combustion    and    in    kind  of  fuel.     In 
any  given  boiler,  within  a  wide  range  of  which  the  limits  are 
usually    far   outside    of   practical    conditions,  the    greater   the 
quantity  of  fuel  burned  the  less  the  amount  of  steam  made  per 
unit  weight    of   that    fuel  ;    the  smaller  the  quantity  of  fuel, 
burned  under  proper  conditions,  in  the  boiler,  the  higher  the 
efficiency ;  and  it  has  been  seen    in   an    earlier   chapter,    that 
the  gain  in  efficiency,  with  increasing  proportion  of  heating  to 
grate  surface  or  to  fuel  burned,  is  less  and  less  as  this  increase 
goes  on.     By  enlarging  or  reducing  the  grate,  or  by  increasing 
or  diminishing  the  draught  and  air-supply,  and  during  a  suc- 
cession of  trials,  noting  the  method  of  variation  of  efficiency 
and  of  capacity  for  making  steam,  the  law  of  such  variations 


49°  THE   STEAM-BOILER. 

may  be  established,  and  the  best  arrangement,  all  things  con- 
sidered, may  be  determined. 

252.  Variations  of  Proportions  in  different  boilers,  other- 
wise similar,  have  been  seen  to  be  capable  of  expression  by  a 
very  simple  algebraic  expresssion  on  which  all  theories  of  effi- 
ciency are  based.     But  in  some  cases  this  law  is  not  found  to 
be    precisely    applicable,   and    only    test-trials    of    boilers    so 
differing    can  be  relied  upon  to  give  correct  relations.      The 
general  relations  already  stated   invariably  hold  ;  but  it  often 
happens  that  a  steam-boiler  exhibits  peculiarities  which  make 
that  exact  statement  inapplicable.     It  is  not  uncommon   not 
only  to  compare    actual  performance,  as  shown  by  trial,  with 
the  results  indicated  by  the  theory,  but  also  to  alter  the  ratio 
of  heating  to  grate  surface  by  bricking  over  more  or  less  of 
the  grate,  and  by   this    or   other   expedients  so   varying  that 
ratio  in  successive  trials  as  to  obtain  an  empirical  and  approxi- 
mately exact  expression  for  the  law  of  variation  of  efficiency 
for  the  particular  case  in  hand. 

253.  Combined  Power  and  Efficiency  distinguish  the  best 
types  of  boiler.     That  which,  at  a  given  cost,  exhibits  highest 
steam-producing  power  combined  with  greatest  efficiency,  is 
the  best  boiler.     These  qualities,  however,  are  not  usually  com- 
patible, and  increased  steam-production  from  any  boiler  is  com- 
monly attended  with  a  decrease  in  efficiency;  and  as  the  one  or 
the  other  of  these  qualities  is  the  more  important,  the  combi- 
nation which  will  give  best  total  result  will  vary.     In   no  two 
cases  will  the  same  combination  be  equally  desirable.     Every 
boiler  must  be  tested  for  both  before  it  can  be  said  whether  it 
is  satisfactorily  adapted  to  its  place  and  work. 

254.  The  Apparatus  and  Methods  of  test-trials  should  be 
prescribed  in  the  preliminary  arrangements  for  every  trial,  and 
if  possible  should  be  in  exact  accordance  with  some  accepted 
standard  rules.     The  apparatus  consists  of  scales  and  tanks  for 
measurement  of  weights  of  coal  and  of  water  ;  gauges  to  give 
the  pressure  of  steam  ;    thermometers    of   great    accuracy    to 
determine   the   temperatures  of  water,  steam,  and   flue-gases  ; 
and  calorimeters  to  determine  the  quality  of  the  steam  and 


STEAM-BOILER    TRIALS.  491 

the  extent  of  superheating,  or  the  percentage  of  moisture  en- 
trained by  it. 

The  establishment  of  the  correctness  of  this  apparatus  is  the 
first  of  the  preliminaries  to  their  use.  The  standardization 
of  the  instruments  is  a  matter  of  supreme  importance,  since 
upon  their  accuracy  the  whole  work  of  the  engineer  is  depend- 
ent. It  is  also  a  work  demanding,  in  most  cases,  unusual  skill 
and  care,  and,  to  be  satisfactory,  must  generally  be  performed 
either  at  the  manufacturer's,  or  at  the  office  of  the  engineer 
conducting  the  trial.  The  scales  can  usually  be  standardized 
by  the  official  sealer  of  weights  and  measures,  and  sealed  by 
him  ;  the  water-meters,  if  used,  can  be  readily  tested  by  the  use 
of  the  scales  so  sealed  ;  the  thermometers  are,  as  a  rule,  best 
tested  by  their  makers,  and  should  be  sent  to  the  maker  for 
test  immediately  before  and  directly  after  the  test.  The 
engineer  often  has  a  carefully  preserved  standard  with  which 
they  may  be  compared  in  his  own  office.  The  same  remarks 
apply  to  the  examination  of  the  gauges  used,  which  should  be 
standardized  both  before  and  after  their  use.  The  apparatus 
used  in  connection  with  the  calorimeter,  in  the  determina- 
tion of  the  quality  of  the  steam  made,  demand  exceptional 
care  in  this  process.  Where  it  is  unavoidable,  the  use  of 
coarsely  graduated  thermometers  and  roughly  constructed 
scales  may  be  permitted,  but  only  then  when  a  very  large 
number  of  observations  are  taken,  and  an  average  thus  ob- 
tained which  may  befairly  expected  to  fall  within  reasonable 
limits  of  error. 

The  method  of  starting  and  of  stopping  the  trial  is  a  very 
important  matter,  and  one  upon  which  engineers  of  experience 
and  acknowledged  authority  are  not  in  complete  accord.  The 
principles  to  be  adhered  to  in  this  matter,  as  in  every  other 
detail  of  the  operation  of  testing  a  boiler,  are  easily  specified, 
but  they  are  not  always  as  easy  of  practice.  All  conditions 
should  be  as  exactly  the  same  at  the  beginning  and  at  the  end 
of  the  test  as  they  can  possibly  be  made.  The  period  of  the 
trial  and  the  times  of  stopping  and  of  starting  should  be  capa- 
ble of  being  exactly  fixed,  and  the  method  of  test  should  be 


492  THE    STEAM-BOILER. 

such  as  should  permit  of  the  commencement  and  the  end 
occurring  at  these  exactly  defined  times,  or,  as  an  alterna- 
tive, they  should  be  such  that  the  work  done  by  the  boiler 
during  the  less  precisely  determinable  time  of  beginning  and 
ending  of  the  trial  should  be  as  nearly  as  possible  nil,  so 
that  a  slight  error  as  to  time  may  not  appreciably  affect  the 
results. 

During  the  trial,  provision  should  be  made  for  the  preserva- 
tion of  the  utmost  possible  uniformity  of  working  conditions 
throughout  the  whole  period  of  the  trial.  Every  irregularity 
gives  rise  to  more  or  less  loss  of  efficiency,  and  to  uncertainty 
in  regard  to  the  correctness  of  the  reported  figures.  The  nearer 
the  working  of  the  boiler  is  kept  to  the  final  average  for  the 
trial,  the  better. 

Uniformity  of  operation  and  maximum  efficiency  are  best 
attainable  during  a  trial  when  a  system  of  record  is  adopted 
which  allows  of  that  regularity  being  shown  at  all  times  ;  and 
records  in  proper  form  are  the  best  possible  security  against 
error  of  observation.  Graphical  methods  should  be  adopted 
wherever  practicable.  Such  methods  of  record  exhibit  most 
satisfactorily  the  accordance  with  or  the  deviation  from  the 
uniformity  of  operation  considered  so  desirable  on  the  score  of 
efficiency  and  accuracy. 

255.  Standard  Test-trials  are  made  under  established  sys- 
tems, and  in  accordance  with  codes  of  regulations  which  are 
accepted  as  representing  a  satisfactory  system  of  procedure. 
In  such  cases  the  first  step  is  to  settle  upon  a  standard  of 
measurement  and  comparison  that  may  be  accepted  by  all  who 
may  be  interested  in  the  result.  The  standard  nominal  horse- 
power has  already  been  described  as  now  accepted  by  the  best 
authorities. 

The  Committee  of  Judges  of  the  Centennial  Exhibition,  to 
whom  the  trials  of  competing  boilers  at  that  exhibition  were 
intrusted,  adopted  the  unit,  30  pounds  of  water  evaporated  into 
dry  steam  per  hour  from  feed-water  at  100°  Fahrenheit,  and  un- 
der a  pressure  of  seventy  pounds  per  square  inch  above  tJie  atmos- 
phere, these  conditions  being  considered  to  represent  fairly 


STEAM-BOILER    TRIALS.  493 

average  practice.  The  quantity  of  heat  demanded  to  evaporate 
a  pound  of  water  under  these  conditions  is  1 1 10.2  British  ther- 
mal units,  or  1.1496  "  units  of  evaporation."  The  unit  of  power 
proposed  is  thus  equivalent  to  the  development  of  33,305  heat- 
units  per  hour,  or  34.488  units  of  evaporation.  The  "  unit  of 
evaporation"  is  taken  as  a  certain  weight — preferably  unity  of 
water,  evaporated  "  from  and  at  "  the  boiling-point  under  atmos- 
pheric pressure.  The  now-accepted  unit  of  boiler-power,  in  the 
code  constructed  for  the  American  Society  of  Mechanical  En- 
gineers,* is  the  equivalent  of  the  Centennial  Standard,  and  in 
ail  standard  trials  the  commercial  horse-power  is  taken  as  an 
evaporation  of  30  pounds  of  water  per  hour  from  a  feed-water 
temperature  of  100°  Fahr.  into  steam  at  70  pounds  gauge-pres- 
sure, which  is  equal  to  34^  units  of  evaporation,  that  is,  to  34^- 
pounds  of  water  evaporated  from  a  feed-water  temperature  of 
212°  Fahr.  into  steam  at  the  same  temperature.  This  standard 
is  equal  to  33,305  thermal  units  per  hour.f 

A  boiler  rated  at  any  stated  horse-power  should  be  capable 
of  developing  that  power  with  easy  firing,  moderate  draught 
and  ordinary  fuel,  while  exhibiting  good  economy ;  and  the 
boiler  should  be  capable  of  developing  one  half  or  one  third 
more  than  its  rated  power  to  meet  emergencies  at  times  when 
maximum  economy  is  not  the  most  important  object  to  be  at- 
tained. 

256.  Instructions  and  Rules  governing  the  standard  sys- 
tem of  boiler-trial,  prepared  by  a  committee  of  the  American 
Society  of  Mechanical  Engineers,  may  be  taken  as  a  good  illus- 
tration of  such  regulations  as,  in  one  form  or  another,  have 
been  customarily  agreed  upon  by  engineers  conducting  such 
work.  They  are  as  follows  : 


*  Transactions,  vol.  vi.,  1884. 

f  An  evaporation  of  30  pounds  of  water  from  100°  F.  into  steam  at  70  pounds 
pressure  is  equal  to  an  evaporation  of  34.488  pounds  from  and  at  212°;  and  an 
evaporation  of  34^  pounds  from  and  at  212°  F.  is  equal  to  30.010  pounds  from 
100°  F.,  into  steam  at  70  pounds  pressure. 

The  "unit  of  evaporation"  being  equal  to  965.7  thermal  units,  the  commercial 
horse-power  is  34.488  X  965.7  =  33-3O5  thermal  units. 


494  THE   STEAM-BOILER. 

PRELIMINARIES   TO   A   TEST. 

I.  In  preparing  for  and  conducting  trials  of  steam-boilers, 
the  specific  object  of  the  proposed  trial  should  be  clearly  defined 
and  steadily  kept  in  view. 

II.  Measure  and  record  the  dimensions,  position,  etc.,  of  grate 
and  heating  surfaces,  flues  and  chimneys,  proportion  of  air-space 
in  the  grate-surface,  kind  of  draught,  natural  or  forced. 

III.  Put  the  Boiler  in  good  condition. — Have  heating-surface 
clean  inside  and  out,  grate-bars  and  sides  of  furnace  free  from 
clinkers,  dust  and  ashes  removed  from  back  connections,  leaks 
in  masonry  stopped,  and  all  obstructions  to  draught  removed. 
See  that  the  damper  will  open  to  full  extent,  and  that  it  may 
be  closed  when  desired.     Test  for  leaks  in  masonry  by  firing  a 
little  smoky  fuel  and  immediately  closing  damper.    The  smoke 
will  then  escape  through  the  leaks. 

IV.  Have  an  understanding  with  the  parties  in  whose  inter- 
est the  test  is  to  be  made  as  to  the  character  of  the  coal  to  be 
used.     The  coal  must  be  dry,  or,  if  wet,  a  sample  must  be  dried 
carefully  and  a  determination  of  the  amount  of  moisture  in  the 
coal  made,  and  the  calculation  of  the  results  of  the  test  corrected 
accordingly. 

Wherever  possible,  the  test  should  be  made  with  standard 
coal  of  a  known  quality.  For  that  portion  of  the  country 
east  of  the  Alleghany  Mountains  good  anthracite  egg  coal 
or  Cumberland  semi-bituminous  coal  may  be  taken  as  the 
standard  for  making  tests.  West  of  the  Alleghany  Mountains 
and  east  of  the  Missouri  River,  Pittsburg  lump  coal  may  be 
used.* 

V.  In  all  important  tests  a  sample  of  coal  should  be  selected 
for  chemical  analysis. 

VI.  Establish  the  correctness  of  all  apparatus  used  in  the  test 
for  weighing  and  measuring.     These  are : 

*  These  coals  are  selected  because  they  are  almost  the  only  coals  which  con- 
tain the  essentials  of  excellence  of  quality,  adaptability  to  various  kinds  of  fur- 
naces, grates,  boilers,  and  methods  of  firing,  and  wide  distribution  and  general 
accessibility  in  the  markets. 


STEAM-BOILER    TRIALS.  495 

1.  Scales  for  weighing  coal,  ashes,  and  water. 

2.  Tanks,  or   water-meters    for   measuring   water.     Water- 
meters,  as  a  rule,  should  only  be  used  as  a  check  on  other  meas- 
urements.    For  accurate  work,  the  water  should  be  weighed  or 
measured  in  a  tank. 

3.  Thermometers  and  pyrometers   for  taking  temperatures 
of  air,  steam,  feed-water,  waste  gases,  etc. 

4.  Pressure-gauges,  draught-gauges,  etc. 

VII.  Before  beginning  a  test,  the  boiler  and  chimney  should 
be  thoroughly  heated  to  their  usual  working  temperature.     If 
the  boiler  is  new,  it  should  be  in  continuous  use  at  least  a  week 
before  testing,  so  as  to  dry  the  mortar  thoroughly  and  heat  the 
walls. 

VIII.  Before  beginning  a  test,  the  boiler  and  connections 
should  be  free  from  leaks,  and  all  water-connections,  including 
blow  and  extra-feed  pipes,  should  be  disconnected  or  stopped 
with  blank   flanges,  except   the  particular  pipe  through  which 
water  is  to  be  fed  to  the  boiler  during  the  trial.     In  locations 
where  the  reliability  of  the  power  is  so  important  that  an  extra 
feed-pipe  must  be  kept  in  position,  and  in  general  when  for  any 
other  reason  water-pipes  other  than  the  feed-pipes  cannot  be 
disconnected,  such  pipes  may  be  drilled  so  as  to  leave  openings 
in  their  lower  sides,  which  should  be  kept  open  throughout  the 
test  as  a  means  of  detecting  leaks,  or  accidental  or  unauthorized 
opening  of  valves.     During  the  test  the  blow-off  pipe  should 
remain  exposed. 

If  an  injector  is  used,  it  must  receive  steam  directly  from  the 
boiler  being  tested,  and  not  from  a  steam-pipe,  or  from  any 
other  boiler. 

See  that  the  steam-pipe  is  so  arranged  that  water  of  con- 
densation cannot  run  back  into  the  boiler.  If  the  steam-pipe 
has  such  an  inclination  that  the  water  of  condensation  from  any 
portion  of  the  steam-pipe  system  may  run  back  into  the  boiler, 
it  must  be  trapped  so  as  to  prevent  this  water  getting  into  the 
boiler  without  being  measured. 


49^  THE   STEAM-BOILER. 

STARTING  AND   STOPPING   A   TEST. 

A  test  should  last  at  least  ten  hours  of  continuous  running, 
and  twenty-four  hours  whenever  practicable.  The  conditions 
of  the  boiler  and  furnace  in  all  respects  should  be,  as  nearly  as 
possible,  the  same  at  the  end  as  at  the  beginning  of  the  test. 
The  steam-pressure  should  be  the  same,  the  water-level  the 
same,  the  fire  upon  the  grates  should  be  the  same  in  quantity 
and  condition,  and  the  walls,  flues,  etc.,  should  be  of  the  same 
temperature.  To  secure  as  near  an  approximation  to  exact 
uniformity  as  possible  in  conditions  of  the  fire  and  in  tempera- 
tures of  the  walls  and  flues,  the  following  method  of  starting 
and  stopping  a  test  should  be  adopted : 

X.  Standard  Method. — Steam  being  raised  to  the  working 
pressure,  remove  rapidly  all  the  fire  from  the  grate,  close  the 
damper,  clean  the  ash-pit,  and  as  quickly  as  possible  start  a  new 
fire  with  weighed  wood  and  coal,  noting  the  time  of  starting 
the  test  and  the  height  of  the  water-level  while  the  water  is  in 
a  quiescent  state,  just  before  lighting  the  fire. 

At  the  end  of  the  test,  remove  the  whole  fire,  clean  the 
grates  and  ash-pit,  and  note  the  water-level  when  the  water  is 
in  a  quiescent  state ;  record  the  time  of  hauling  the  fire  as  the 
end  of  the  test.  The  water-level  should  be  as  nearly  as  pos- 
sible the  same  as  at  the  beginning  of  the  test.  If  it  is  not  the 
same,  a  correction  should  be  made  by  computation,  and  not  by 
operating  pump  after  test  is  completed.  It  will  generally  be 
necessary  to  regulate  the  discharge  of  steam  from  the  boiler 
tested  by  means  of  the  stop-valve  for  a  time  while  fires  are 
being  hauled  at  the  beginning  and  at  the  end  of  the  test,  in 
order  to  keep  the  steam-pressure  in  the  boiler  at  those  times 
up  to  the  average  during  the  test. 

XL  Alternate  Method. — Instead  of  the  Standard  Method 
above  described,  the  following  may  be  employed  where  local 
conditions  render  it  necessary  : 

At  the  regular  time  for  slicing  and  cleaning  fires  have 
them  burned  rather  low,  as  is  usual  before  cleaning,  and  then 
thoroughly  cleaned ;  note  the  amount  of  coal  left  on  the 
grate  as  nearly  as  it  can  be  estimated  ;  note  the  pressure  of 


STEAM-BOILER    TRIALS.  497 

steam  and  the  height  of  the  water-level — which  should  be  at 
the  medium  height  to  be  carried  throughout  the  test — at  the 
same  time  ;  and  note  this  time  as  the  time  of  starting  the  test. 
Fresh  coal,  which  has  been  weighed,  should  now  be  fired.  The 
ash-pits  should  be  thoroughly  cleaned  at  once  after  starting. 
Before  the  end  of  the  test  the  fires  should  be  burned  low,  just 
as  before  the  start,  and  the  fires  cleaned  in  such  a  manner  as  to 
leave  the  same  amount  of  fire,  and  in  the  same  condition,  on  the 
grates  as  at  the  start.  The  water-level  and  steam-pressure 
should  be  brought  to  the  same  point  as  at  the  start,  and  the 
time  of  the  ending  of  the  test  should  be  noted  just  before  fresh 
coal  is  fired. 

DURING   THE   TEST. 

XII.  Keep  the  Conditions  Uniform. — The  boiler  should  be 
run  continuously,  without  stopping  for  meal-times  or  for  rise 
or  fall  of  pressure  of  steam  due  to  change  of  demand  for  steam. 
The  draught  being  adjusted  to  the  rate  of  evaporation  or  com- 
bustion desired  before  the  test  is  begun,  it  should  be  retained 
constant  during  the  test  by  means  of  the  damper. 

If  the  boiler  is  not  connected  to  the  same  steam-pipe  with 
other  boilers,  an  extra  outlet  for  steam  with  valve  in  same 
should  be  provided,  so  that  in  case  the  pressure  should  rise  to 
that  at  which  the  safety-valve  is  set,  it  may  be  reduced  to  the 
desired  point  by  opening  the  extra  outlet,  without  checking 
the  fires. 

If  the  boiler  is  connected  to  a  main  steam-pipe  with 
other  boilers,  the  safety-valve  on  the  boiler  being  tested  should 
be  set  a  few  pounds  higher  than  those  of  the  other  boilers,  so 
that  in  case  of  a  rise  in  pressure  the  other  boilers  may  blow  off, 
and  the  pressure  be  reduced  by  closing  their  dampers,  allowing- 
the  damper  of  the  boiler  being  tested  to  remain  open,  and  firing 
as  usual. 

All  the  conditions  should  be  kept  as  nearly  uniform  as  pos- 
sible, such  as  force  of  draught,  pressure  of  steam,  and  height  of 
water.  The  time  of  cleaning  the  fires  will  depend  upon  the 
character  of  the  fuel,  the  rapidity  of  combustion,  and  the  kind 
of  grates.  When  very  good  coal  is  used,  and  the  combustion 
not  too  rapid,  a  ten-hour  test  may  be  run  without  any  cleaning 

2-2 


49^  THE   STEAM-BOILER. 

of  the  grates,  other  than  just  before  the  beginning  and  just  be- 
fore the  end  of  the  test.  But  in  case  the  grates  have  to  be 
cleaned  during  the  test,  the  intervals  between  one  cleaning  and 
another  should  be  uniform. 

XIII.  Keeping  the  Records. — The  coal  should  be  weighed 
and  delivered  to  the  firemen  in  equal  portions,  each  sufficient 
for  about  one  hour's  run,  and  a  fresh  portion  should  not  be  de- 
livered until  the  previous  one  has  all  been  fired.     The   time 
required  to  consume  each  portion  should  be  noted,  the  time  be- 
ing recorded  at   the  instant   of  firing  the  first  of  each  new  por- 
tion.    It  is  desirable  that  at  the  same  time  the  amount  of  water 
fed  into  the  boiler  should  be  accurately  noted  and  recorded,  in- 
cluding the  height  of  the  water  in  the  boiler,  and  the  average 
pressure  of  steam  and  temperature  of  feed  during  the  time.    By 
thus  recording  the  amount  of  water  evaporated  by  successive 
portions  of  coal,  the  record  of  the  test  may  be  divided  into  sev- 
eral divisions,  if  desired,  at  the  end  of  the  test,  to  discover  the 
degree  of  uniformity  of  combustion,  evaporation,  and  economy 
at  different  stages  of  the  test. 

XIV.  Priming  Tests. — In  all  tests  in  which  accuracy  of  re- 
sults is  important,  calorimeter  tests  should  be  made  of  the  per- 
centage of  moisture  in  the  steam,  or  of  the  degree  of  super- 
heating.    At  least  ten  such  tests  should  be  made  during  the 
trial  of  the  boiler,  or  so  many  as  to  reduce  the  probable  average 
error  to  less  than   one  per  cent,  and  the  final  records  of  the 
boiler  test  corrected    according  to  the  average  results  of   the 
calorimeter  tests. 

On  account  of  the  difficulty  of  securing  accuracy  in  these 
tests  the  greatest  care  should  be  taken  in  the  measurements  of 
weights  and  temperatures.  The  thermometers  should  be  ac- 
curate to  within  a  tenth  of  a  degree,  and  the  scales  on  which 
the  water  is  weighed  to  within  one  hundredth  of  a  pound. 

ANALYSES   OF   GASES. — MEASUREMENT   OF  AIR-SUPPLY,    ETC. 

XV.  In  tests  for  purposes  of  scientific  research,  in  which  the 
determination  of  all  the  variables  entering  into  the  test  is  de- 
sired, certain  observations  should  be  made  which  are  in  general 
not  necessary  in  tests  for  commercial  purposes.     These  are  the 
measurement  of  the  air-supply,  the    determination  of  its  con- 


STEAM-BOILER    TRIALS. 


499 


tained  moisture,  the  measurement  and  analysis  of  the  flue- 
gases,  the  determination  of  the  amount  of  heat  lost  by  radiation, 
of  the  amount  of  infiltration  of  air  through  the  setting,  the 
direct  determination  by  calorimeter  experiments  of  the  absolute 
heating  value  of  the  fuel,  and  (by  condensation  of  all  the  steam 
made  by  the  boiler)  of  the  total  heat  imparted  to  the  water. 

The  analysis  of  the  flue-gases  is  an  especially  valuable 
method  of  determining  the  relative  value  of  different  methods 
of  firing,  or  of  different  kinds  of  furnaces.  In  making  these 
analyses  great  care  should  be  taken  to  procure  average  samples, 
since  the  composition  is  apt  to  vary  at  different  points  of  the 
flue,  and  the  analyses  should  be  intrusted  only  to  a  thoroughly 
competent  chemist,  who  is  provided  with  complete  and  accurate 
apparatus. 

As  the  determination  of  the  other  variables  mentioned  above 
are  not  likely  to  be  undertaken  except  by  engineers  of  high 
scientific  attainments,  and  as  apparatus  for  making  them  is 
likely  to  be  improved  in  the  course  of  scientific  research,  it  is 
not  deemed  advisable  to  include  in  this  code  any  specific  direc- 
tions for  making  them. 

RECORD   OF  THE   TEST. 

XVI.  A  "  log"  of  the  test  should  be  kept  on  properly  pre- 
pared blanks,  containing  headings  as  follows  : 


PRESSURES. 

TEMPERATURES. 

FUEL. 

FEED- 
WATER. 

TIME. 

L: 

1 

rt 

i 

u 

1 

1 

0 

a 

-    

M 

PQ 

Steam-g 

1 

Q 

Externa 

1 

i 

c 

T3 

1 

rt 
9 

C/5 

1 

Pounds. 

g 

H 

Pounds  < 





BOO 


THE   STEAM-BOILER. 


REPORTING  THE  TRIAL. 

XVII.  The  final  results  should  be  recorded  upon  a  properly 
prepared  blank,  and  should  include  as  many  of  the  following 
items  as  are  adapted  for  the  specific  object  for  which  the  trial 
is  made.  The  items  marked  with  a  *  may  be  omitted  for  or- 
dinary trials,  but  are  desirable  for  comparison  with  similar  data 
from  other  sources. 


Results  of  the  trials  of  a. 

Boiler  at , 

To  determine 


hours. 

DIMENSIONS    AND    PROPORTIONS. 

Leave  space  for  complete  description.     See  Ap- 
pendix XXIII. 
3.  Grate-  surf  ace.  .  .  .wide.  .  .  .long.  .  .  .Area.  .  .  . 

sq.  ft. 
sq.   ft. 

^    Superheating-surface                          

sq.  ft. 

6.   Ratio  of  water  heating  surface  to  grate-sur- 

AVERAGE  PRESSURES. 

7    Steam-pressure  in  boiler   by  gauge               . 

Ibs. 

*8    Absolute  steam-pressure                          

Ibs. 

*q    Atmospheric  pressure   per  barometer  

in. 

in. 

AVERAGE   TEMPERATURES. 

deer 

ucg. 

deer 

ucg. 

dee:. 

IA    Of  escaping  gases     .          

deer 

deer 

FUEL. 

16    Total  amount  of  coal  consumed  \           ..... 

Ibs 

17    Moisture  in  coal                                          

per  cent 

18     Dry  coal  consumed                      

Ibs 

19.  Total  refuse,  dry  pounds  =  
20.  Total  combustible  (dry  weight  of  coal,  Item 
18    less  refuse    Item   IQ)               

per  cent. 
Ibs 

Ibs. 

*22.  Combustible  consumed  oer  hour.  . 

Ibs. 

*  See  reference  in  paragraph  preceding  table. 

f  Including  equivalent  of  wood  used  in  lighting  fire.  I  pound  of  wood 
equals  0.4  pound  coal.  Not  including  unburnt  coal  withdrawn  from  fire  at  end 
of  test. 


STEAM-BOILER    TRIALS. 


501 


RESULTS    OF    CALORIMETRIC   TESTS. 

23.  Quality  of  steam,  dry  steam  being  taken  as 

unity 

24.  Percentage  of  moisture  in  steam per  cent. 

25.  Number  of  degrees  superheated deg. 

WATER. 

26.  Total  weight  of  water  pumped  into   boiler 

and  apparently  evaporated  * Ibs. 

27.  Water    actually   evaporated,    corrected    for 

quality  of  steam  f Ibs. 

28.  Equivalent  water  evaporated  into  dry  steam 

from  and  at  212°  F.f Ibs. 

2g.  Equivalent   total  heat   derived  from  fuel  in 

British  thermal  units  f B.  T.  U. 

30.  Equivalent  water  evaporated  into  dry  steam 

from  and  at  212°  F.  per  hour Ibs. 

ECONOMIC    EVAPORATION. 

31.  Water  actually  evaporated  per  pound  of  dry 

coal,   from  actual   pressure  and   tempera- 
ture f  Ibs. 

32.  Equivalent  water  evaporated   per  pound  of 

dry  coal  from  and  at  212°  F.f Ibs. 

33.  Equivalent  water  evaporated  per  pound  of 

combustible  from  and  at  212°  F.f Ibs. 


*  Corrected  for  inequality  of  water-level  and  of  steam-pressure  at  beginning 
and  end  of  test. 

f  The  following  shows  how  some  of  the  items  in  the  above  table  are  de- 
rived from  others: 

Item  27  =  Item  26  X  Item  23. 

Item  28  =  Item  27  X  Factor  of  evaporation. 

J-T  —    h 

Factor  of  evaporation  =  ,  ^Tand  h  being  respectively  the  total  heat- 

units  in  steam  of  the  average  observed  pressure  and  in  water  of  the  average 
observed  temperature  of  feed,  as  obtained  from  tables  of  the  properties  of  steam 
and  water. 

Item  29  =  Item  27  X  (ff  —  h}. 

Item  31  =  Item  27  -f-  Item  18. 

Item  32  =  Item  28  -|-  Item  18  or  =  Item  31  X  Factor  of  evaporation. 

Item  33  =  Item  28  -4-  Item  20  or  =  Item  32  -*-  (per  cent  100  —  Item  19). 

Items  36  to  38.     First  term  =  Item  20  X  - 
Items  40  to  42.     First  term  =  Item  39  X  0.8698. 

Item  43  —  Item  29  X  0.00003  °r  = ~. 

34i 
_  Difference  of  Items  43  and  44 

Item  45  — - ' ? • 

Item  44. 


502 


THE  STEAM-BOILER. 


COMMERCIAL    EVAPORATION. 

34.  Equivalent  water  evaporated  per    pound  of 

dry  coal  with  one  sixth  refuse,  at  70  pounds 
gauge-pressure,  from  temperature  of  100° 
F.  =  Item  33  multiplied  by  0.7249  Ibs. 

RATE   OF   COMBUSTION. 

35.  Dry  coal  actually  burned  per  square  foot  of 

grate-surface  per  hour Ibs. 

i"j  Per  sq.  ft.   of  grate- 
Consumption  of   |       surface. . ,    Ibs. 
dry  coal  per  hour.    I  Per  sq.  ft.  of  water- 
Coal  assumed  with   |      heating  surface.. ..         Ibs. 
one  sixth    refuse. f      Per   sq.    ft.    of    least 
j      area  for  draught. . .         Ibs. 

RATE    OF   EVAPORATION. 

39.  Water  evaporated  from  and  at  212°   F.  per 

square  foot  of  heating-surface  per  hour. .  .         Ibs. 
f      Water  evaporated   J  Per  sq.  ft.  of  grate- 

"Mo     !  Per  nour  from  tem-          surface Ibs. 

*li     \  Perature  °f   I00°  F-    I  Per  S<1-  ft-  °f  water- 
*A2      '  into     steam     °f    7°   f     heating  surface.  .         Ibs. 
J  pounds    gauge-pres-    |  Per  sq.  ft.  of  least 
[sure.f  j      area  for  draught.         Ibs. 

COMMERCIAL   HORSE-POWER. 

43.  On  basis  of  thirty  pounds  of  water  per  hour 

evaporated  from  temperature  of  100°  F. 
into  steam  of  70  pounds  gauge  pressure, 
(  =  34i  Ibs.  from  and  at  212°)  f H.  P. 

44.  Horse-power,  builders' rating,  at square 

feet  per  horse-power H.   P. 

45.  Per    cent    developed  above,  or  below,   rat- 

ing f Per  cent. 


257-  Precautions  are  to  be  taken  in  every  possible  way  to 
prevent  and  avoid  irregularities  in  the  conduct  of  the  trial  and 
errors  of  observation.* 

In  preparing  for  and  conducting  trials  of  steam-boilers  the 
specific  object  of  the  proposed  trial  should  be  clearly  defined 
and  steadily  kept  in  view,  and  as  suggested  by  Mr.  Hoadley — 

(i)  If  it  be  to  determine  the  efficiency  of  a  given  style  of 
boiler  or  of  boiler-setting  under  normal  conditions,  the  boiler 
brickwork,  grates,  dampers,  flues,  pipes,  in  short,  the  whole  ap- 
paratus, should  be  carefully  examined  and  accurately  described, 

*  The  appendix  to  the  report  above  quoted  should  be  read  in  this  connection. 


STEAM-BOILER    TRIALS.  503 

and  any  variation  from  a  normal  condition  should  be  remedied, 
if  possible,  and  if  irremediable,  clearly  described  and  pointed  out. 

(2)  If  it  be  to  ascertain  the  condition  of  a  given  boiler  or 
set  of  boilers  with  a  view  to  the  improvement  of  whatever  may 
be  faulty,  the  conditions  actually  existing  should  be  accurately 
observed  and  clearly  described. 

(3)  If  the  object  be  to  determine  the  relative  value  of  two 
or  more  kinds  of  coal,  or  the  actual  value  of  any  kind,  exact 
equality  of   conditions  should    be    maintained  if     possible,    or, 
where  that  is  not  practicable,  all  variations  should  be  duly  al- 
lowed for. 

(4)  Only  one  variable  should  be  allowed  to  enter  into  the 
problem ;  or,  since  the  entire  exclusion  of  disturbing  variations 
cannot  usually  be  effected,  they  should  be    kept  as  closely  as 
possible  within  narrow  limits,  and  allowed  for  with  all  possible 
accuracy. 

Blanks  should  be  provided  in  advance,  in  which  to  enter  all 
data  observed  during  the  test.  The  preceding  instructions 
contain  the  form  used  in  presenting  the  general  results.  Rec- 
ords should  be,  as  far  as  possible,  made  in  a  standard  form,  in 
order  that  all  may  be  comparable. 

The  observations  must  be  made  by  the  engineer  conduct- 
ing the  trial,  or  by  his  assistants,  with  this  object  distinctly  in 
mind ;  and  each  should  have  a  well-defined  part  of  the  work 
assigned  him,  and  should  assume  responsibility  for  that  part, 
having  a  distinct  understanding  in  regard  to  the  extent  of 
his  responsibility,  and  a  good  idea  of  the  extent  and  nature 
of  the  work  done  by  his  colleagues,  and  the  relations  of  each 
part  to  his  own.  No  observations  should  be  permitted  to  be 
made  by  unauthorized  persons  for  entrance  upon  the  log ; 
and  no  duties  should  be  permitted  to  be  delegated  by  one  as- 
sistant to  another,  without  consultation  and  distinct  under- 
standing with  the  engineer  in  charge.  The  trial  should,  wher- 
ever possible,  be  so  conducted  that  any  error  that  may  occur  in 
the  record  may  be  detected,  checked,  or,  if  advisable,  removed, 
by  some  process  of  mutual  verification  of  related  observations. 
It  is  in  this  direction  that  the  use  of  graphical  methods  of  rec- 
ord and  automatic  instruments  have  greatest  value. 


5O4  THE   STEAM-BOILER. 

Several  methods  of  weighing  fuel  have  been  found  very  satis- 
factory, but  it  should  be  an  essential  feature  that  the  weights 
shall  be  made  by  one  observer  and  checked  by  another,  at  as 
distant  a  point  as  is  convenient.  The  weighing  of  the  fuel  by 
one  observer  at  the  point  of  storage,  and  the  record  at  that 
point  of  times  of  delivery,  as  well  as  of  weights  of  each  lot,  and 
the  tallying  of  the  number  and  record  of  the  time  of  receipt  at 
the  furnace-door,  will  be  usually  found  a  safe  system.  The  fail- 
ure to  record  any  one  weight  leads  to  similar  error,  and  can 
only  be  certainly  prevented  by  an  effective  method  of  double 
observation  and  check. 

The  same  remarks  apply,  to  a  considerable  extent,  to  the 
weighing  of  the  water  fed  to  the  boiler.  A  careful  arrangement 
of  weighing  apparatus,  a  double  set  of  observations,  where  pos- 
sible, and  thus  safe  checks  on  the  figures  obtained,  are  essential 
to  certainty  of  results.  With  good  observers  at  the  tank,  and 
with  small  demand  for  water,  a  single  tank  can  be  used  ;  but 
two  are  preferable  in  all  cases,  and  three  should  be  used  if  the 
work  demands  very  large  amounts  of  feed-water,  as  at  trials  of 
very  large  boilers,  or  ^f  "  batteries."  The  more  uniform  the 
water-supply,  as  well  as  the  more  steady  the  firing,  the  less  the 
liability  to  mistake  in  making  the  record. 

The  two  blanks  which  follow  were  prepared  by  the  Author 
for  use  in  laboratory  as  well  as  professional  work. 

258.  The  Results  of  Trials  actually  conducted  under  ac^ 
ceptable  conditions,  and  with  all  the  precautions  which  have 
been  advised,  are  illustrated  by  the  following  examples : 

The  first  case  was  a  trial  which  was  carried  out  in  ac- 
cordance with  the  above  programme.  The  measurements  of 
the  feed-water  were  made  by  passing  the  water  through  a 
Worthington  metre  into  two  wooden  tanks  located  on  Fair- 
banks Standard  Platform  Scales.  The  pipe  connections  were 
so  arranged  that  one  tank  could  be  filled  and  weighed 
while  the  other  tank  was  being  emptied  into  the  boiler. 

Each  tank  was  filled  once  every  half  hour.  As  soon  as  the 
tank  was  full  and  the  pumping  into  the  boiler  commenced,  the 
temperature  of  the  feed-water  was  taken  by  sensitive  ther- 
mometers reading  to  one-tenth  of  a  degree. 


STEAM-BOILER    TRIALS. 


505 


cc 


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H 

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§• 

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SUPER- 
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f 
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JO  3SB1U3O43J 

X 
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oiui  una  taBajs 

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J  -  J.  =  H 

CDB91S   OJ04J  }«3H 

/?  =y  XyM 

•43J3U1UOIB3  OJ 
P94J3JSUE4J  JB3H 

HEAT-UNITS 
PER  POUND 

FROM 

BOILER. 

X 
•ureais 

; 

•J35B^V\. 

CALORIMETER. 

TEMPERATURE. 

^7 
§- 
«  u 

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WEIGHTS. 

lls 

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Condensing 
Water. 

W 

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H 

1 

506 


STEAM-BOILER. 


on  Composition 

W 

9 

M 

S 

(4 

5 

REAL  EVAPORATION. 

Square  feet  of  Heat- 
ing-surface required 
to  Evaporate  one 
Cubic  Foot  of  Water. 

•34nSS34d-mB31S 

IBmoB     IB    PUB    •  j 

{ 

•^    0ZIZ  IB 
PUB    UJO4J  }U3[BAinb3 

} 

IVXOJL 

1 

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43JBAV-p33J     JO     34m 
-B43dUI31  (BniDB  UJO4JJ 

1 

3j 

uoiuodo4cj 

t) 

i 

Per  Square  Foot  of 
Heating-surface,  per 
Hour. 

•34nSS34d-UIB31S 
IBmOB       }B     pUB      '  J 

9ziz  ujo4j  ^usiBAinbg 

1 

•IBJOX 

i 

CONSUMPTION  OF 
FUEL.  | 

unoq  43d 

30BJ4nS 
-3upB3£J  JO 
'Ij'-bS    43J 

i 

PUB  uio4j  ;u3iBAinbg 

| 

*34nSS34d 
-UIB31S  |BmOB  IB  pUB 
431BA\-p33J    JO     34m 
-B43dUI3^  [BniDB  UIO4^J 

1 

unoq 

JO   JOOJ 
34BnbS  43J 

jQ 

Per  Pound  of  Com- 
bustible. 

•34nSS34d-UIB31S 

lBn;oB    JB     PUB    -a 
aziz  uio4j  lusjBAinog 

1 

•HUM,  |  | 

•g  Oziz  5B 

I 

AVERAGE 
PRESSURES. 

•ffSSwa 

1 

-01B3JS  |BmDB  >B  pUB 
431BA\-p33J    JO    34ttl 
-B43dCU3J  JBmDB  UIO4jJ 

1 

•3J3nBJ3      1  e/j 

-UJB31S   1  = 

U3}3UIO4Bg 

M 

C 

Per  Pound  of  Fuel. 

|BmDB     3B     pUB     '  J 

1 

AVERAGE 

TEMPERATURES. 

U3JEM. 
-P39J 

•A"3uujiq3 

OJ  30UB4^Ug 

1 

PUB  OJO4J  !U3[BAinbg 

I 

•34nSS34d 
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-UJB33S  IBmOB  }B  pUB 
J3JBAV-P33J    JO    34  m 
-B43dai31  |BmOB  OT04J 

i 

AREAS. 

JO  UOIJD3S 
-SS043  ;SB3^ 

sr 

Per  Pound  of  Com- 
bustible. 

IBnjoB    ve    pne  -jj 

I 

•3DBJ4nS 

-43dng 

1 

PUB  rao4j  3U3iBAinbg 

I 

•9DBJ4nS 
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-B43dlU31  |«mDB  UlOJjJ 

l 

'31B4Q 

1 

JO    HXON3q 

e 

3 
0 
ffi 

Per  Pound  of  Fuel. 

'34nSS34d-UlB31S 
JBmOB     IB       pUB      'J 

Oziz  rao4j  lusjEAinbg 

l 

puB  rao4j  ;u3iHAinbg 

I 

"IV1HJ,  JO    3J.VQ 

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-UIB31S  ^BmOB  IB  pUB 
431BM-P33J    JO   34m 
-B43dlU3J  [BmOB  UIO4jJ 

i 

'1VMX 

jo   aaawnj^ 

1 

STEAM-BOILER   TRIALS. 


SO/ 


Equivalent 
from  212°  F. 
and  at 
actual  steam- 
pressure. 


«* 

>  rt  o 

'i.8  s 


MO 
O  Z 


I* 


Sfc'      I.: 


c  «« 


3  E 

erg 


1 

HORSE-POWER. 

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•pai*H 

'8+tffl  v  =d     CQ 
NI  ff  dNV  y  do  samvA  ^ 

EFFICIENCY. 

•paremnsg 

'IBjuauiuadxa 

•pajBunjsg 

per  cent. 

•pnaamuadxg 

per  cent. 

EVAPORATION  FROM  AND  AT  212°  F., 
EQUIVALENT  TO  TOTAL  HEAT-UNITS 

DERIVED  FROM  FUEL. 

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jgd  3D^jjns-Sui 
-jean  jo  •};  -bs  jaj 

1 

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jo'punoj  J3<j 

1 

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jo  punoj  aaj 

1 

•SuiiuatLiadns 
jo  itmocuv  aSBJ3AV 

1 

5O8  THE    STEAM-BOILER. 

The  measurements  of  the  coal  were  effected  by  weighing 
the  coal  previous  to  its  being  wheeled  into  a  pile  in'  the  coal- 
room.  The  second  weighing  was  made  when  the  coal  was  fed 
into  the  furnace.  As  far  as  it  was  possible,  the  furnace  was 
supplied  with  coal  at  intervals  of  every  half  hour,  so  as  to 
correspond  as  nearly  as  could  be  to  the  feeding  of  the  water. 

After  the  completion  of  the  test,  a  careful  analysis  of  the 
coal  was  made,  to  determine  upon  a  sufficiently  large  scale  its 
calorific  power  and  the  quantity  of  contained  moisture.  The 
steam  from  the  boiler  was  condensed  by  means  of  a  continu- 
ously acting  calorimeter,  formed  by  placing  four  tanks  on 
Fairbanks  Standard  Platform  Scales.  The  steam  from  the 
boiler  was  passed  through  a  surface-condenser  having  a 
condensing  surface  of  63 1  sq.  ft.  As  fast  as  the  steam  was  con- 
densed from  the  boiler  it  was  received  in  small  tanks  located 
on  platform-scales.  These  tanks  were  similar  in  size  to  the 
feed-water  tanks,  and  were  so  arranged  as  to  be  filled  and 
emptied  once  every  half  hour,  one  tank  receiving  the  condensed 
water  from  the  boiler  while  the  other  was  being  emptied. 

The  condenser  was  supplied  with  a  large  volume  of  cold 
water  from  a  weir  just  outside  of  the  works,  and  after  flowing 
through  the  condenser  and  thereby  cooling  the  steam  and 
receiving  therefrom  the  contained  heat,  this  water  was  caught 
in  two  large  tanks  placed  on  platform-scales.  These  tanks  were 
also  arranged  so  that  one  tank  could  be  emptied  while  the 
other  was  being  filled,  and  were  of  sufficient  capacity  so  as  to 
insure  catching  all  of  the  water  required  for  half  an  hour's  run 
in  the  condenser.  The  temperature  of  the  inlet  water  of  the 
condenser,  of  the  outlet  water,  and  of  the  condensed  steam 
were  carefully  noted  by  means  of  thermometers  reading  to  a 
tenth  of  a  degree.  Readings  of  the  inlet  water  and  of  the 
condensed  steam  were  taken  once  every  half  hour  at  the 
same  time  that  the  quantities  of  the  water  in  the  tanks  were 
weighed.  Inasmuch  as  the  outlet  to  the  condenser  varied 
considerably  in  temperature,  readings  on  this  were  taken  every 
five  minutes  during  the  entire  time  of  the  test.  It  will  thus  be 
seen  that  a  very  correct  average  of  the  amount  of  heat  given  to 
the  condenser  was  obtained.  The  quantity  of  air  supplied 


STEAM-BOILER    TRIALS. 

by  the  blowers  to  the  furnace  was  measured  by  continuously 
acting  anemometers  placed  in  the  supply-pipes.  The  readings 
of  the  anemometers  were  checked  by  means  of  the  number  of 
revolutions  of  the  blowers  and  their  cubic  feet  per  revolution. 

The  steam-pressure  was  kept  by  a  recording  pressure-gauge, 
which  was  checked  by  an  exceedingly  delicate  and  sensi- 
tive gauge,  which  previously,  and  subsequently  to  the  test, 
was  carefully  verified  by  means  of  a  mercury  column.  Constant 
records  of  the  hygrometer,  barometer,  and  thermometers,  both 
in  the  boiler-room  and  of  the  external  air,  were  kept  during  the 
entire  period  of  the  test. 

It  will  be  seen  from  the  above,  that  all  of  the  processes  and 
measurements  were  kept  in  duplicate  in  such  a  way  as  to  afford 
a  constant  check  on  each  other  and  preclude  the  possibility  of 
any  errors. 

Samples  of  steam  were  taken  in  a  small  calorimeter  for  the 
purpose  of  ascertaining  whether  the  boiler  supplied  wet  steam. 

The  following  is  a  brief  condensed  summary : 

EFFICIENCY  AS  PER  TEST,  7.50  A.M.  to  7. 50  A.M. 

Total  heat  of  boiler 64,536,613  heat-units. 

Steam 42,933,141  "  "  66.6  per  cent. 

Heat  escaping  in  flue-gases.. ..   9,669,036  "  "  15  "  " 

Radiated  heat 5,162,939  "  "  8  "  " 

Heat  to  vaporize   moisture  in 

coal 141,372  "  "  0.2  "  " 

Heat  to  vaporize   moisture  in 

air  supplied  to  furnace 345,978  "  "  0.4  "  " 

Leakage 3,531,645  "  "  4-O  "  " 

"       from  pump 127,936  "  "  0.2  "  " 

Heat  absorbed  by  fire-brick 2,581,645  "  "  4.0  "  " 

Unaccounted  for 1,092,941  "  "  1.6  "  " 

In  the  trial  of  an  upright  boiler  reported  on  by  Sir  Frederick 
Bramwell,  in  1876,  coke  being  used  as  the  fuel  and  wood  in 
starting  the  fires,  the  following  data*  were  obtained : 

Ash  and  moisture 43-79  lbs- 

Combustible. 194.46 

Total  fuel 238.25     " 

Air  used  per  pound  combustible I7i  ' ' 

*  Conversion  of  Heat  into  Work.     Anderson. 


5io 


THE    STEAM-BOILER. 


Heat  generated,  net 2,798,312  B.  T.  u. 

"                        per  Ib.  fuel n>745  "   " 

"             "           available,  net 2,101,700  "  " 

Water  evaporated 1,620  Ibs. 

The  efficiency  of  the  furnace  was o.  643  ' ' 

The  balance-sheet  stands  thus : 

Dr. 

Available  heat , 2, 101 , 700  B.  T.  u. 

Cr. 
Per  Cent. 

88.29     Heat  expended  in  evaporation 1,855,900  B.  T.  u. 

7.03     Displacing  atmosphere .147,720  "   " 

3.35     Loss  by  conduction  and  radiation 70,430  "   " 

.05     Heatinashes 1,129  "  " 

Unaccounted  for 25,521  "   " 


1.26 


100.00 


2,101,700 

The  following  are  data  from  a  trial  of  a  Galloway  boiler, 
as  reported  to  the  Edgemoor  Iron  Co.,  in  the  year  1885, 
by  Messrs.  G.  N.  Comly  and  R.  Dawes,  and  the  efficiency 
too  near  the  theoretical  maximum  to  be  often  duplicated. 
The  boiler  tested  was  fitted  with  an  "  economizer,"  or  feed- 
water  heater,  and  the  power  developed  was  considerably  under 
its  rating.  The  fuel  was  a  Pennsylvania  bituminous.  The 
draught  was  obtained  by  a  high  chimney,  and  was,  as  shown  in 
the  table,  quite  powerful.  The  tabular  statement  is  mainly 
given  as  illustrating  a  very  compact  form  of  record  of  results. 

TABLE   OF    RESULTS   OF   THE   TEST   OF   A   GALLOWAY   BOILER  AT 
FRANKFORD    JUNCTION,  PHILADELPHIA,  PA. 


DIMENSIONS 

AND 

PROPORTIONS: 


AVERAGE 
PRESSURES: 


Date  of  Trial . 

Duration  of  Trial 

Height  of  Stack 

Boiler,  seven    feet    in   diameter,  twenty-eight 
feet  long. 

Grate-surface     .         .        .        .         .        .        . 

Water-heating-surface                                   . 
Superheating-surface           . 
Ratio  of  Water-heating  Surface  to  Grate-sur- 
face       

Economizer    Heating-surface,  per  each   boiler 

'Force  of  Draught,  in  inches,  at    stack  base, 

after  leaving  economizer     .... 

Force  of  Draught,  in  inches*  at  back  of  boiler, 

before  entering  economizer          .         .         . 

Force  of  Draught,  in  inches,  at  front  of  boiler, 

before  entering  economizer 

Absolute  Steam-pressure 

Atmospheric  Pressure,  per  barometer 
[  Steam-pressure  in  boiler,  by  gauge 


April  8th,  1885. 
1 1*4  hours. 
200  feet. 


35.75  sq.  ft. 

853 
225 

23.86  to  i  sq.  ft. 
609  sq.  ft. 


.75  ins.  of  water. 
.5625 

.6063 

93-575  pounds. 
29.975  inches. 
78.875  pounds. 


STEAM-BOILER    TRIALS. 


AVERAGE 
TEMPERATURES:  ^ 


FUEL: 


RESULTS  OF 

CALORIMETRIC 

TESTS: 


WATER: 


ECONOMIC 
EVAPORATION; 


Of  External  Air 

Of  Fire-room      ....... 

Of  Steam 

Of  Chimney-flue,  escaping  gases 

Of  Side-flue,  at  back  end  of  boiler,  escaping 

gases   ........ 

Of  Side-flue,  at  front  end  of  boiler,  escaping 

gases   

Of  Feed-water 

Of  Feed-water,   after  leaving  economizer,  and 

entering  boiler     ...... 

Total  amount  of  Coal  consumed 

Total  Refuse  from  coal 

Moisture  in  Coal        ...... 

Total  Combustible 

Dry  Coal  consumed,  per  hour   . 

Combustible  consumed,  per  hour 

Dry  Coal  consumed,  per  indicated  horse-power, 
per  hour  ....... 

Combustible  consumed,  per  indicated  horse- 
power, per  hour 

f  Quality  of  Steam,  dry  steam  being  taken  as 
J          unity   ........ 

|  Percentage  of  Moisture  in  steam 
L  Number  of  Degrees  superheated 

Height  of  Water  in  gauge-glasses      . 
Total  weight  of  Water  pumped  into  boiler 

Of  this  there  was  used  as  hot  water     . 
Converted  into  Steam 

Water  actually  evaporated,  corrected  for  qual- 
ity of  steam.         ...... 

Equivalent  Water  evaporated  into  dry  steam 

from  and  at  212°  F 

Percentage  of  increase  of  Evaporative  Capacity 

by  using  economizer 

Equivalent  Water  evaporated  into  dry  steam 

from  and  at  212°  F.  per  hour     . 
Equivalent   total  Heat   derived   from   fuel,   in 

British  thermal  units 

Equivalent  total  Heat  derived  from  one  pound 

of  dry  coal 

Equivalent  total  Heat  derived  from  one  pound 

of  combustible     ...... 

Water  actually  evaporated,  per  pound  of  dry 
coal,  from  actual  pressure  and  temperature 

Water  actually  evaporated,  per  pound  of  com- 
bustible ....... 

Equivalent  Water  evaporated,  per 
pound  of  dry  coal,  from  and  at 
212°  F. 

Equivalent  Water  evaporated,  per 
pound  of  combustible,  from 
and  at  212°  F. 

Equivalent  Water  evaporated,  per 
pound  of    combustible, 
and  at  212°  F.          .          .          .    \      mizer. 


Boiler  and 
Economizer 

used 
together. 


By  boiler, 
fromJ  exclusive 
m  1  ofecono- 


IDry  Coal  actually  burned,  per  square  foot  of 
grate-surface,  per  hour        .... 
Consumption  of  dry  f  Per  square  foot  of  grate- 
Coal  per  hour,  coal  j      surface 
assumed   with  one  |  Per      square     foot      of 
sixth  refuse,  (  water-heating  surface  . 


58  degrees. 
66 
381        " 

200  " 

360  « 

589  " 

84  « 

155  " 

6925  pounds. 

569 

301 
6055 


1.87   " 
1.72   " 

1.019984. 

None. 

58  degrees. 

4.63  inches. 
68, 138  pounds. 

2,782        " 
65,356        " 

66,854        " 
78,112        " 

6^5  per  cent. 
\  6943  pounds. 
|  116  cubic  feet. 

75.432885. 
.11389. 
.12459. 

10.093  pounds. 


11.041 

"•793 
12.907 

12.153 

16.46 
18.07 
o-745 


5I2 


THE    STEAM-BOILER. 


RATE  OF 
EVAPORATION: 


Water  evaporated  from  and  at  212°  F.,  per 
square  foot  of  water-heating  surface,  per 
hour  ........ 

Water  evaporated,  per  hour,  f  Per  square  foot 
from  temperature  of  of  grate-surface 
100°  F.  into  steam  of  4  Per  square  foot 
seventy  pounds'  gauge-  of  water-heat- 
l  in] 


pressure, 


ing  surface 


Horse-power  of  engine,  as  per  indicator-cards 
taken  on  day  of  boiler-test 

Kind  of  Coal  used      ...... 

Condition  of  Chimney-damper  .... 

Cleaned  fires,  number  of  times  on  each  fur- 
nace during  the  test 


8. 139    pounds. 
168.9  " 

7.079        » 


311-45  horse-power. 
Ocean  bituminous. 
58  p.c.  of  full  open'g. 


In  trials  conducted  by  the  Author,  for  a  committee  of  the 
American  Institute,  of  which  he  was  chairman,  in  testing  a 
number  of  different  types  of  boiler,*  a  surface-condenser  was 
employed  to  condense  all  steam  made,  and  results  thus  for  the 
first  time  obtained  which  gave  exact  measures  of  net  efficiency, 
the  quality  of  all  steam  made  being  determined. 

In  calculating  the  results  from  the  record  of  the  logs,  the 
committee  first  determined  the  amount  of  heat  carried  away  by 
the  condensing  water  by  deducting  the  temperature  at  which  it 
entered  from  that  at  which  it  passed  off.  To  this  quantity  is 
added  the  heat  which  was  carried  away  by  evaporation  from 
the  surface  of  the  tank,  as  determined  by  placing  a  cup  of 
water  in  the  tank  at  the  top  of  the  condenser  at  such  height 
that  the  level  of  the  water  inside  and  outside  the  cup  were  the 
same,  noting  the  difference  of  temperatures  of  the  water  in  the 
cup  and  at  the  overflow,  and  the  loss  by  evaporation  from  the 
cup.  The  amount  of  evaporation  from  the  surface  of  the 
water  in  the  cup  and  in  the  condenser,  which  latter  was  ex- 
posed to  the  air,  was  considered  as  approximately  proportional 
to  the  tension  of  vapor  due  their  temperatures,  and  was  so 
taken  in  the  estimate.  The  excess  of  heat  in  the  water  of  con- 
densation over  that  in  the  feed-water  also  evidently  came  from 
the  fuel,  and  this  quantity  was  also  added  to  those  already 
mentioned. 


*  See  Transactions,  1871;  also,  Report  on  Mechanical  Engineering  at  Vienna 
International  Exhibition,  1873,  R.  H.  T. 


STEAM-BOILER   TRIALS.  513 

The  total  quantities  were,  in  thermal  units,  as  follows : 

A 34,072,058.09 

B 48,241,833.60 

C 24,004,601.14 

D 38,737,217.57 

E 11,951,002.10 

These  quantities,  being  divided  by  the  weight  of  combus- 
tible used  in  each  boiler  during  the  test,  will  give  a  measure  of 
their  relative  economical  efficiency;  and,  divided  by  the  num- 
ber of  square  feet  of  heating-surface,  will  indicate  their  relative 
capacity  for  making  steam.  But  as  it  was  the  intention  of  the 
committee  to  endeavor  to  establish  a  practically  correct  meas- 
ure that  should  serve  as  a  standard  of  comparison  in  subsequent 
trials,  it  was  advisable  to  correct  these  amounts  by  ascertaining 
how  and  where  errors  have  entered,  and  introducing  the  proper 
correction.  There  were  two  sources  of  error  that  are  considered 
to  have  affected  the  result  as  above  obtained.  The  tank  being 
of  wood,  a  considerable  quantity  of  water  entered  it,  leaked  out 
again  at  the  bottom,  without  increase  of  temperature,  instead 
of  passing  through  the  tank  and  carrying  away  the  heat,  as  it 
is  assumed  to  have  done  in  the  above  calculation.  The  meters 
also  registered  rather  more  water  than  actually  passed  through 
them,  and  this  excess  assists  in  making  the  above  figures  too 
high.  The  sum  of  these  errors  the  committee  estimated  at 
4  per  cent  of  the  total  quantity  of  heat  carried  away  by  the 
condensing  water.  The  other  two  quantities  were  considered 
very  nearly  correct. 

Making  these  deductions,  we  have  the  following  as  the  total 
heat,  in  British  thermal  units,  which  was  thrown  into  the  con- 
denser by  each  boiler : 

A 32,751, 835 . 34 

B 46,387,827.10 

C 23,066,685 . 39 

D 37,228,739.07 

E i 1,485, 777 . 35 

That  the  figures  thus  obtained  are  very  accurate,  is  shown 
by  calculating  the  heat  transferred  to  the  condenser  by  the 
Root  and  the  Allen  boilers  (both  of  which  superheated  their 

33 


5H  THE   STEAM-BOILER. 

steam),  by  basing  the  calculation  on  the  temperature  of  the 
steam  in  the  boiler,  as  given  by  the  thermometer,  the  results 
thus  obtained  being  32,723,681.76  and  46,483,322.5,  respec- 
tively. 

Dividing  these  totals  by  the  pounds  of  combustible  con- 
sumed by  each  boiler,  we  get  as  the  quantity  of  heat  per  pound, 
and  as  a  measure  of  the  relative  economic  efficiency : 

A 10,281.53 

B 10. 246 . 92 

C 10,143.66 

D 10,048.24 

E "... 10,964.94 

Determining  the  weight,  in  pounds,  of  water  evaporated  per 
square  foot  of  heating-surface  per  hour,  we  get  as  a  measure  of 
the  steaming  capacity : 

A 2.65 

B 3-59 

C 2.83 

D ..3.10 

E 1.92 


The  quantity  of  heat  per  pound  of  combustible,  as  above 
determined,  being  divided  by  the  latent  heat  of  steam  at  212° 
Fahrenheit  (966°.6),  gives  as  the  equivalent  evaporation  of 
water  at  the  pressure  of  the  atmosphere,  and  with  the  feed  at  a 
temperature  of  212°  Fahrenheit: 

A 10.64 

B 10. 60 

C 10.49 

D 10.40 

E 10.34 

For  general  purposes  this  is  the  most  useful  method  of  com- 
parison for  economy. 

The  above  figures  afford  a  means  of  comparison  of  the 
boilers,  irrespective  of  the  condition  (wet  or  dry)  of  the  steam 
furnished  by  them.  All  other  things  being  equal,  however, 
the  committee  consider  that  boiler  to  excel  which  furnishes  the 
driest  steam ;  provided  that  the  superheating,  if  any,  does  not 
exceed  about  100°. 


STEAM-BOILER    TRIALS.  515 

In  this  trial  the  superheating  was  as  follows : 

A i6°.o8 

B 13°. 23 

C o. 

D o. 

E o. 

As  the  boilers  C,  D,  E  did  not  superheat,  it  became  an  inter- 
esting and  important  problem  to  determine  the  quantity  of 
water  carried  over  by  each  with  the  steam.  This  we  are  able, 
by  the  method  adopted,  to  determine  with  great  facility  and 
accuracy. 

Each  pound  of  saturated  steam  transferred  to  the  condens- 
ing water  the  quantity  of  heat  which  had  been  required  to 
raise  it  from  the  temperature  of  the  water  of  condensation  to 
that  due  to  the  pressure  at  which  it  left  the  boiler,  plus  the  heat 
required  to  evaporate  it  at  that  temperature.  Each  pound  of 
water  gives  up  only  the  quantity  of  heat  required  to  raise  it 
from  the  temperature  of  the  water  of  condensation  to  that  of 
the  steam  with  which  it  is  mingled.  The  total  amount  of  heat 
is  made  up  of  two  quantities,  therefore,  and  a  very  simple 
algebraic  equation  may  be  constructed  which  shall  express  the 
conditions  of  the  problem : 

Let 

H  —  heat-units  transferred  per  pound  of  steam. 
h  =  heat-units  transferred  per  pound  of  water. 
U  =  total  quantity  of  heat  transferred  to  condenser. 
W  =  total  weight  of  steam  and  water,  or  of  feed-water. 
x  =  total  weight  of  steam. 
W—x  =  total  weight  of  water  primed. 

Then 

+  h(W—x)=  U',or  x  =  * 


H 

h 

Substituting  the  proper  values  in  this  equation,  we  deter- 


Si6 


THE   STEAM-BOILER. 


mine  the  absolute  weights  and  percentages  of  steam  and  water 
delivered  by  the  several  boilers  as  follows : 


Weight  of  Steam. 

Weight  of  Water. 

Percentage  of  Water 
Primed  to  Water 
Evaporated. 

A  

27,896. 

o. 

O. 

B                   

•2Q    6?O 

o. 

O. 

c         

iq  782.04 

645  .  06 

3.26 

D  

1l,66l.  35 

2,336.65 

6.0 

E                             .  .     .. 

a  Sqt;  6 

2o6  .  Q 

q 

And  the  amount  of  water,  in  pounds,  actually  evaporated 
per  pound  of  combustible  : 


8.76 
8.76 
8.70 

8.55 
9.41 


Comparing  the  above  results,  the  committee  were  enabled 
to  state  the  following  order  of  capacity  and  of  economy  in  the 
boilers  exhibited,  and  their  relative  percentage  of  useful  effect, 
as  compared  with  the  economical  value  of  a  steam-boiler  that 
should  utilize  all  of  the  heat  contained  in  the  fuel : 


Steaming  Capacity. 

Economy  of  Fuel. 

Percentage 
of 
Economical  Effect. 

A  

No.  4 

No.  2 

O.  7OQ 

B  

No    i 

No   3 

O   7O7 

C  

No    3 

No    4 

o  699 

D  

No   2 

No.  5 

o  6cn 

E  

No.  5 

No.  i 

o  7c;6 

The  results  obtained  as  above,  and  other  very  useful  deter- 
minations derived  from  this  extremely  interesting  trial,  were 
given  in  the  table,  as  a  valuable  standard  set  of  data  with  which 
to  compare  the  results  of  future  trials,  and  as  a  useful  aid  in 
judging  of  the  accuracy  of  statements  made  by  boiler-venders 
in  the  endeavor  to  effect  sales  by  presenting  extravagant  claims 
of  economy  in  fuel. 

Mr.  Drewitt  Halpin  found  the  following  net  results  of  test  of 
a  variety  of  English-built  boilers : 


STEAM-BOILER    J^RIALS. 


517 


POUNDS  WATER 
EVAPORATED. 

THERMAL  UNITS. 

il 

"o  o 

"3    (N 

5  « 

.  <t> 

£*! 

. 

II  u 

No. 

DESCRIPTION  OF 
BOILER. 

11 
u  <"  u 

"o  « 

-—  .  *O 

•c^    . 

3 

y>g^t 

ill 

^  a  w 

3   rt  £ 

tl  j;  b£3 
Bu-S^ 

T3 
C 

I 

ogr'3 

&S'a 

eA  ct  u 

"  <u  a> 

flj-C   ^ 

II! 

"w 

J3 

t«  3  ti 
=  o  S  fc 
2^=J=  a 

b 

- 
*o 

IE 

f|| 

£ 

£ 

C 

H 

£ 

W 

£ 

j 

Field    . 

4  *  57 

8  83 

4  414 

8,529 

Field 

2.28 

U  .  UJ 

jo  8^? 

2,202 

10.461 

Field  

2.57 

1U.UJ          | 

10  93     i 

2,482 

10.558 

4 
5 
6 
7 

Portable  \  %*  
Portable  (  ~  
Portable  f..}i   
Portable  )  0  

1.52 

2.26 
1.76 
3-56 

10.23 
10.49 
11.81 
9-93 

14.718 

14,718 
14,718 

1,468 
2,183 
1,700 
3,438 

9.882 
10,133 
11.408 
9,592 

67 
68 
77 

98.356 

148.444 
130  900 
118.248 

g 

Lancashire 

1  .  57 

12    83 

T  C   71  C 

T.Cl6 

TO    OQO 

77 

108  248 

9 

Lancashire  

2.83 

i^.Oj 

9.89 

Ow  *  J 

13,833 

±.^  AU 

2,733 

i"t^5?J 

9-553 

68 

i8.s,844 

10 

Lancashire 

1.88 

12     2^         ' 

15*715 

1,816 

ii  8^q 

7^ 

i  ^6.200 

ii 

Jacketed  

4.70 

i^  .  4$         i 

7-7 

14.805 

4»5Q5 

a  •L,°oo 
7.500 

/O 

50 

229.750 

12 

Lancashire  

2-57 

10.9 

2,482 

10.529 

67 

166.294 

-jg 

Compound  

1-43 

11.51 

14,296 

1,381 

11.125 

78 

107.7:8 

14 
15 

Loco.  (Webb)  
Loco.  (Marie)  

9.83 
4.62 

10.28 
10.65 

14.004 
14.600 

9,495 
4,462 

9,930 
10,287 

7° 

70 

664.650 
312.340 

16 

Loco,  j 

8.22 

13.550 

12,142 

7.940 

58 

704,236 

18 

L°co-  (-Coke 

•f:P 

8-94 
IO.OI 

13,550 
13,550 

13.263 

8,636 
9,669 

i    63 
71 

8,5.569 
463.630 

Loco,  f  ^ 

*9 

Loco.  ) 

7-39 

II.  2 

7,138 

10,819 

77 

549.626 

20 

Torpedo  

12.54 

8-37 

14,727 

12,113 

8,085 

54 

654,102 

21 

Torpedo  

*•*    O<r 

14.86 

7.78 

M,354 

7,523 

51 

732-°54 

22 

Torpedo  ... 

17.90 

7-49 

14,727 

17,291 

7,235 

49 

847-259 

23 

Torpedo  

20.74 

7.04 

14,727 

20,034 

6.800 

46 

921,564 

24 

a 

b 

C 

d 

e 

/ 

£ 

The  "  locomotive"  boiler  is  found  to  be  more  efficient  as  a 
part  of  the  engine  and  on  the  track  than  when  mounted  as  a 
stationary  boiler,  an  unexpected  result. 

259.  The  Quality  of  Steam  made  in  any  boiler,  or  as  sup- 
plied to  an  engine,  is  hardly  less  important  than  the  quantity. 
When  the  steam  is  required  for  heating  purposes  simply,  or 
even  when  all  the  heat  issuing  as  waste,  necessary  or  other, 
from  the  exhaust-ports  of  a  non-condensing  engine  cylinder 
can  be  utilized  for  useful  and  paying  purposes,  this  is  a  matter 
of  no  importance;  but  when  it  is  essential  that  loss  in  the 
engine  shall  be  made  a  minimum,  and  that  the  engine  shall 
have  maximum  efficiency,  the  quality  of  the  steam  becomes 
exceedingly  important.  Dry  steam  is  very  much  more  efficient 
as  a  working  substance  in  the  steam-engine  than  wet ;  since, 
where  the  latter  is  supplied  from  the  boiler,  the  waste  by 
cylinder-condensation  is  greatly  increased — and  so  greatly  that 
the  more  obvious  direct  loss  by  the  passing  of  heat  through 
the  engine  in  unavailable  form,  hot  water  acting  as  its  vehicle, 
becomes  comparatively  small.  The  determination  of  the  quality 


518  THE   STEAM-BOILER. 

of  steam  by  any  boiler  is  thus  as  important  as  the  measure  of 
its  apparent  evaporation. 

The  difference  between  the  apparent  and  the  actual  evapo- 
ration is  often  very  great.  A  good  boiler  properly  managed 
will  usually  "  prime"  less  than  five  per  cent,  even  though 
having  no  superheating-surface,  and  less  than  two  per  cent 
may  usually  be  hoped  for.  Steam  is  often  made  practically 
dry.  But  a  hard-worked  boiler,  or  one  having  defective  circu- 
lation, will  often  prime  ten  or  twenty  per  cent ;  and  cases  have 
been  found  in  the  experience  of  the  Author  in  which  the  quan 
tity  of  water  carried  out  of  the  boiler  by  the  current  of  steam  ex- 
ceeded the  weight  of  the  steam  itself.  It  has  thus  happened 
that,  where  no  measure  of  this  defect  has  been  made,  the 
apparent  evaporation  only  being  reported,  the  quantity  of  water 
said  to  have  been  evaporated  has  equalled,  and  sometimes  has 
even  greatly  exceeded,  the  theoretically  possible  evaporation  of 
an  absolutely  perfect  boiler.  It  is  thus  essential  that,  when  the 
apparent  evaporation  has  been  determined  by  trial,  the  quantity 
of  water  entrained  with  the  steam  be  measured  and  deducted,  and 
then  real  evaporation  thus  ascertained  and  reduced  for  the 
standard  conditions.  Under  ordinarily  good  conditions,  a  real 
evaporation  of  ten  or  eleven  times  the  weight  of  the  fuel,  cor- 
responding to  an  efficiency  of  0.75  to  0.80,  represents  the  best 
practice,  and  a  real  evaporation  of  twelve  of  water  by  one  of 
combustible,  from  and  at  the  boiling-point,  or  an  efficiency  of 
eighty  per  cent,  is  rarely  observed  under  the  usually  best  con- 
ditions of  steam-boiler  practice.  Where  more  than  the  efficiency 
here  given  as  probable  is  reported,  the  work  should  be  very  care- 
fully revised,  and  errors  sought  until  absolute  certainty  is 
secured. 

Trials  not  including  calorimetric  measurement  of  the  water 

o 

entrained  with  the  steam  are  comparatively  valueless,  and 
should  be  rejected  in  any  important  case.  Reports  of  extra- 
ordinary economy  are  often  based  on  this  kind  of  error.  The 
experiments  of  M.  Hirn  at  Mulhouse  showed  an  average  of  about 
5  per  cent  priming  ;  Zeuner  makes  it  approximately  from  /-J  to 
15  per  cent;  while  the  experiments  of  the  Author  at  the 
American  Institute  in  1871  give  from  3  to  6.9  per  cent. 


STEAM-BOILER    TRIALS.  519 

A  recently  devised  method  of  measuring  the  amount  of 
moisture  in  the  steam  is  to  introduce  into  the  boiler  with  the 
feed-water  sulphate  of  soda,  and  at  intervals  to  draw  from  the 
lower  gauge-cock  a  small  amount  of  water,  and  also  from  the 
steam,  condensing  either  by  a  coil  of  pipe  in  water  or  a  small 
pipe  in  air.  A  chemical  analysis  gives  the  proportion  of  sul- 
phate of  soda  in  each  portion,  and  the  quotient  of  the  propor- 
tion of  sulphate  of  soda  in  the  portion  from  the  steam  by  the 
proportion  in  that  from  the  water  gives  the  ratio  of  water 
entrained,  as  steam  does  not  carry  sulphate  of  soda,  which  is 
only  brought  over  by  the  hot  water  entrained.  This  method 
was  used  by  Professor  Stahlschmidt  at  the  Diisseldorf  Exhibi- 
tion Trials. 

260.  The  Calorimeters  used  in  determining  the  quantity 
of  moisture  in  steam  have  several  forms,  widely  differing  in 
construction,  and  to  some  extent  in  value.  They  nearly 
all  embody  the  same  principles,  however.  The  objects  sought 
to  be  attained  in  their  construction  are :  The  exact  measure- 
ment of  the  weight  of  steam  received  by  them  from  the  boiler, 
and  of  its  temperature  and  pressure  at  the  boiler ;  the  determi- 
nation of  the  weight  of  water  used  in  its  condensation  and 
the  range  of  temperature  through  which  it  is  raised  in  the 
operation  ;  the  reduction  of  wastes  of  heat  in  the  calorimeter 
to  a  minimum,  and  the  exact  measurement  of  that  waste  if 
it  is  sensibly  or  practically  noticeable. 

The  Barrel  or  Tank  Calorimeter  as  employed  by  the 
Author,  is  the  simplest  form  of  this  instrument  which  has  been 
employed.  It  consists  of  a  strong  barrel  or  tank,  of  hardwood, 
absorbing  little  of  either  water  or  heat,  and  having  a  movable 
cover.  This  tank  is  mounted  on  platform-scales  capable  of 
accurate  adjustment  and  having  as  fine  readings  as  possible.  It 
is  filled  with  water  to  within  about  one  fourth  its  height  from 
the  top,  and  the  steam  is  led  into  it  through  a  rubber  tube  or 
hose  of  sufficient  capacity  to  supply  the  steam  to  the  amount 
of  one  eighth  or  one  tenth  the  weight  of  the  water  in  three 
or  five  minutes.  A  steam-gauge  of  known  accuracy  gives  the 
boiler-pressure,  and  the  corresponding  temperature  and  total 
heat  of  the  steam  are  ascertained  from  the  steam-tables. 


520 


THE   STEAM-BOILER. 


In  using  this  apparatus  the  steam  is  rapidly  passed  into  the 
mass  of  water  contained  in  the  tank,  until  the  scales  show 
that  the  desired  quantity  has  been  added.  The  steam  is  so 
directed  by  varying  the  position  of  the  end  of  the  tube,  and 
by  inserting  it  so  deeply  in  the  water  that  the  whole  mass  is 
very  thoroughly  stirred,  and  a  very  perfect  mixture  secured  of 
condensing  water  with  the  water  of  condensation  ;  and  so  that 
the  temperatures  indicated  by  the  inserted  thermometer  shall 
be  the  real  mean  temperature  of  the  mass.  The  weights  and 


FIG.  118. — THE  CALORIMETER. 

temperatures  are  then  inserted  in  the  log  of  the  trial,  as  below, 
and  the  proportion  of  water  brought  over  with  the  steam  is 
thence  easily  calculable.  The  thermometers  employed  usually 
read  to  tenths  of  a  degree  Fahrenheit,  or  to  twentieths  of  a 
centigrade  degree,  accordingly  as  the  one  or  the  other  scale  is 
employed.  Readings  must  be  made  with  the  greatest  pos- 
sible accuracy,  and  in  sufficient  number  to  insure  a  satis- 
factorily exact  mean.  With  good  thermometers  and  scales, 
a  reliable  gauge,  and  care  in  operation,  good  results  can  be 
obtained  by  averaging  a  series  of  trials.* 

The  Hirn  Calorimeter  is   substantially   the  same   as   the 
above,  with  the  addition  of  an  apparatus  for  stirring  the  water 

*  Report  on  Boiler  Trial,  Trans.  A.  S.  M.  E.  1884,  vol.  vi. 


Sl^EAM-BOILER   TRIALS.  $21 

in  the  tank  to  insure  thorough  mixture  and  readings  of  tem- 
perature of  condensing  water  exactly  representative  of  the  true 
mean  temperature  of  the  mass  after  the  introduction  of  the 
steam.  This  is  not  an  essential  feature  of  the  apparatus,  if  the 
Author  may  judge  by  his  own  experience,  provided  the  jet  of 
entering  steam  is  so  directed  as  to  cause  rapid  circulation. 
No  stirring  apparatus  could  operate  more  efficiently  than 
the  force  of  the  steam  itself,  properly  directed.  Hirn  was 
probably  the  first  (1868)  to  attempt  the  determination  of  the 
quantity  of  steam  as  delivered  from  steam-boilers.*  A  similar 
apparatus  was  used  at  the  trials  of  the  Centennial  International 
Exhibition,  Philadelphia,  i8;6.f 

261.  The  Theory  of  the  Calorimeter  is  as  follows::): 
Each  pound  of  saturated  steam  transferred  to  the  condens- 
ing water  the  quantity  of  heat  which  had  been  required  to 
raise  it  from  the  temperature  of  the  water  of  condensation  to 
that  due  to  the  pressure  at  which  it  left  the  boiler,  plus  the  heat 
required  to  evaporate  it  at  that  temperature.  Each  pound  of 
water  gives  up  only  the  quantity  of  heat  required  to  raise  it 
from  the  temperature  of  the  water  of  condensation  to  that  of 
the  steam,  with  which  it  is  mingled.  The  total  amount  of 
heat  is  made  up  of  two  quantities,  therefore,  and  a  very  simple 
algebraic  equation  may  be  constructed,  which  shall  express  the 
conditions  of  the  problem : 

Let,  as  in  §  258, 

H  —  heat-units  transferred  per  pound  of  steam ; 
h  =  heat-units  transferred  per  pound  of  water ; 
U  =  total  quantity  of  heat  transferred  to  condenser ; 
W  =  total  weight  of  steam  and  water,  or  of  feed-water ; 
x  =  total  weight  of  steam  ; 
W  —  x  —  total  weight  of  water  primed. 

*  Bulletin  de  la  Societe  Industrielle  de  Mulhouse,  1868-9. 

f  Reports  of  Judges,  vol.  vi. 

\  First  published  by  the  Author,  who  had  not  then  become  aware  of  the  work 
done  by  M.  Hirn,  in  Trans.  Am.  Inst.  Report  on  Boiler  Trial,  1871.  See 
also  Vienna  Reports,  vol.  iii.  p.  123. 


522  THE   STEAM-BOILER. 

Then 

U 

7  -w   u_wh 

Hx  +k  (W-x)=U>,wx=-—  -  =H_k 


Substituting  the  proper  values  in  this  equation,  we  deter- 
mine the  absolute  weights  and  percentages  of  steam  and  water 
delivered  by  the  boiler. 

Or,  let 

Q  =  quality  of  the  steam,  dry  saturated  steam  being  unity  ; 
H'  =  total  heat  of  steam  at  observed  pressure  ; 
T  =     "         "     "  water  "  " 

h'  =     "         "     "  condensing  water,  original  ; 
h,   —     "         "     "  "  "      final. 

And  we  have  the  equivalent  expression,  as  written  by  Mr. 
Kent, 


The  value  of  the  quantity  U  is  obtained  by  multiplying  the 
weight  of  water  in  the  calorimeter  originally  by  the  range  of 
temperature  caused  by  the  introduction  of  the  steam  from  the 
boiler.  Mr.  Emery  employs  another  form,  as  below,  in  which 
Q  is  the  quality  of  steam  as  before  ;  W  the  weight  of  con- 
densing water  ;  w  the  weight  added  from  the  boiler  ;  T  the 
temperature  due  the  steam-pressure  in  the  boiler  ;  /  the  initial 
and  /,  the  final  temperature  of  the  calorimeter  ;  /  the  latent 
heat  of  evaporation  of  the  boiler-steam  ;  and  x  the  weight  of 
steam  corresponding  to  /.  Thus, 


and 


*  _ 

w  Iw 


STEAM-BOILER    TRIALS.  $2$ 

If  Q  exceeds  unity,  the  steam  is  superheated  by  the  amount 


0.48 


=  2.o833/(<2-/);* 


and  if  less  than  unity,  the  priming  is,  in  per  cent,  100(1  —  Q). 
262.  Records  of  calorimetric  tests  should  be  even  more 
carefully  and  more  frequently  made  than  in  any  other  part  of 
the  work  of  a  boiler-trial.  The  following,  from  work  conducted 
by  the  Author,  illustrates  the  method.  The  symbols  relate  to 
the  first  of  the  above  formulas. 

PRIMING  TESTS. 


CALORIMETER. 

HEAT-UNITS 

Weights. 

Tempera- 
ture. 

FROM  BOILER. 

111 

Q 
|| 

«| 

M 

if 

. 

ul 

rt  fc  o 

rt  iJ 

rt^ 

rt<"  C 

<u 

*+*  'rt 

H-i 

hri 

£j     «— 

u  CU 

rt 

HH          QJ 

hH 

HH 

^      O 

U 

1 

^ 

8 

Water. 

Steam. 

y 

a 

Q 

a 

01 

c 
0 

•o 

c 
o 

<2g 

1, 

•3 

<uj 

Sti 

t 

T 

=  u 

H 
=  T-t' 

*.y 

- 

# 

H 

c/} 

U 

^ 

~ 

£ 

OS  ^ 

a.m. 

9.46 
10.  16 

2I-5 
38. 

217.6 
218.  i 

14.7   58.9 
15.25  47.8 

123.2  64.3 
121.4  73-6 

262.851 
286.36 

"93-59 
1200.61 

13991.68 

16052.16 

1070.39 
1079.21 

164.96 

12.827 
14.806 

6.3= 

7-20 

11.15 

40. 

250. 

16.65  46.7 

122  .4 

75-7 

288.79 

I2OI  .23 

18925. 

1078.83 

166.39 

17-705 

7-S8 

p.m. 

12.  OI 

72-5 

250. 

18.3 

45-7 

124.2 

78.5 

320.88 

1210.87 

19625. 

1086.67 

196.68 

18.006 

7-77 

I.  01 

61.5  ^50. 

18.2    44.2 

121.  6 

77-4 

311.27 

1808.02 

19350. 

1086.42 

189.67 

17.728 

1  -45 

55-     250. 

18.45  44-6 

I23-7 

79.1 

305-07 

1209.  19 

1082.49 

181.37 

18.231 

7  a? 

2.25 
3.10 

60. 
61.5 

250. 
250. 

18.2    44.2 
16.92  44.6 

122.3  78-1 
121.7  77.1 

309.88 
311.27 

1207  .6l 
1208.02 

19525- 
19275. 

1085.31 
1086.32 

187.58 
189.57 

17.946 
17.917 

7-74 
7.68 

3-55 
4-30 

°5- 

250. 
250. 

I7-1    47-3 
17.1    46.6 

121.4 

120.6 

74-1 
74.0 

3'4-44 
310.81 

1208.96 
1207.88 

18525. 
18500. 

1087.56 
1087.28 

193.04 
190.21 

17.019 
16.996 

7-3«> 
7.29 

The  boiler  was  a  water-tubular  boiler,  which  was  not  so 
handled  as  to  give  as  dry  steam  as  was  desired;  and  one  object 
of  the  trial,  of  which  the  above  is  a  part  of  the  record,  was  to 
ascertain  how  seriously  was  the  quality  of  the  steam  affected. 
It  is  seen  that  the  priming  amounted  to  seven  or  eight  per 
cent,  with  fairly  uniform  figures  through  the  period  of  test.  The 
steam  should  have  entrained  less  than  one  half  this  proportion, 
had  the  boiler  been  all  that  was  expected  of  it. 

Errors  of  small  magnitude,  absolutely,  may  greatly  affect 
the  results  of  calculation,  as  is  well  illustrated  by  the  following 
example  presented  by  Mr.  Kent : 


*  Centennial  Report,  pp.  138-9. 


524  THE   STEAM-BOILER. 

Assume  the  values  of  the  quantities  to  be,  as  read,  column  I  : 


OBSERVED 
READING. 

TRUE 
READING. 

AMOUNT  OF 
ERROR. 

Weight    of     condensing-vvater,     corrected     for 

200  5  Ibs. 

200    Ibs. 

-i-    pound. 

\Veight  of  condensed  steam    w 

9Q      '  ' 

IO  O    '  ' 

yW 

Pressure  of  steam  by  gauge    P 

78 

80        " 

TIT 
2  pounds. 

Original  temperature  of  condensing  water,  /.  .  .  . 
Final  temperature  of  condensing  water,  t'  

44°.  5   " 

I  OO°.  5    " 

45°     " 
100°     " 

i  degree. 

i 

Then  let  it  be  assumed  that  errors  of  instruments  or  of  ob- 
servation have  led  to  the  recording  of  slightly  different  figures 
from  the  true  quantities,  as  given  in  column  2 : 

Moisture        Error 
Substituting  in  the  formula  the      true  per  cent,      per  cent. 

readings,"  we  have  for  the  value  of  Q  =  0.9874  =  1.26  =  o. 

All  readings  true  except  W  =  200.5,  Q  =    .9906  =  0.94  =  0.32 

"         "  "      w   =      9.9,  (?  =  i.oooo  =  o.oo  =1.26 

"         "  "  "      P  =    78.0,  Q=    .9880=1.20  =0.06 

"••*==    44.5,  Q=    .9989  =  0.11  =1.15 

"  "  "         ?."**•-      t'     =100.5,       Q=     .9994  =  0.06        =1.20 

"         "         incorrect Q  =  1.0272  =  (minus)=  3.98 

The  last  case  is  equivalent  to  50.2  degrees  superheating. 

Errors  of  o.i  or  even  0.25  per  cent  in  weights  and  of  tem- 
perature of  equal  amount  not  infrequently  occur,  probably, 
where  ordinary  instruments  are  employed.  The  errors  due 
to  false  weight  in  measurement  of  the  condensed  steam  are 
liable  to  be  very  serious,  and  it  is  only  by  making  a  consider- 
able number  of  observations  and  obtaining  the  mean  that  re- 
sults can  be  secured,  ordinarily,  of  real  value. 

263.  The  "  Coil  Calorimeter"  has  been  devised  to  secure 
more  exact  results  in  the  weighing  of  the  water  of  condensation 
than  can  be  obtained  when  it  is  weighed  as  part  of  the  larger 
mass.  In  this  instrument  a  coil  of  pipe  is  introduced  into  the 
tank  and  serves  as  a  surface-condenser  in  which  the  boiler-steam 
is  received  and  condensed,  and  from  which  it  is  transferred  to 
another  vessel  in  which  it  is  weighed  by  itself  with  scales  con- 
structed to  weigh  such  small  weights  with  accuracy ;  or  the 
coil  is  removed  and  weighed  with  the  contained  water.  In  the 


*  Correction  made  only  for  coil  calorimeter  to  be  described. 


STEAM-BOILER    TRIALS.  525 

former  case,  drops  of  water  may  adhere  to  the  internal  surfaces 
of  the  coil  and  escape  measurement ;  in  the  latter,  the  weight 
to  be  determined  is  increased  by  the  known  weight  of  the  coil, 
and  less  delicacy  of  weighing  becomes  possible. 

The  following  is  Kent's  description  of  his  calorimeter,  which 
is  of  this  class,  and  has  been  found  to  give  good  results :  * 

A  surface-condenser  is  made  of  light-weight  copper  tubing 
f "  in  diameter  and  about  5O/  in  length,  coiled  into  two  coils, 
one  inside  of  the  other,  the  outer  coil  14"  and  the  inner  10"  in 
diameter,  both  coils  being  15"  high.  The  lower  ends  of  the 
coils  are  connected  by  means  of  a  brazed  T-coupling  to  a  shorter 
coil,  about  $'  long,  of  2"  copper  tubing,  which  is  placed  at  the 
bottom  of  the  smaller  coil  and  acts  as  a  receiver  to  contain  the 
condensed  water.  The  larger  coil  is  brazed  to  a  f "  pipe,  which 
passes  upward  alongside  of  the  outer  coil  to  just  above  the  level 
of  the  top  of  the  coil  and  ends  in  a  globe-valve,  and  a  short 
elbow-pipe  which  points  outward  from  the  coil.  The  upper 
ends  of  the  two  f "  coils  are  brazed  together  into  a  T,  and  con- 
nected thereby  to  a  |/x  vertical  pipe  provided  with  a  globe-valve, 
immediately  above  which  is  placed  a  three-way  cock,  and  above 
that  a  brass  union  ground  steam-tight.  The  upper  portion  of 
the  union  is  connected  to  the  steam-hose,  which  latter  is 
thoroughly  felted  down  to  the  union.  The  three-way  cock  has 
a  piece  of  pipe  a  few  inches  long  attached  to  its  middle  outlet 
and  pointing  outward  from  the  coil. 

A  water-barrel,  large  enough  to  receive  the  coil  and  with 
some  space  to  spare,  is  lined  with  a  cylindrical  vessel  of  galva- 
nized iron.  The  space  between  the  iron  and  the  wood  of  the 
barrel  is  filled  with  hair-felt.  The  iron  lining  is  made  to  return 
over  the  edge  of  the  barrel,  and  is  nailed  down  to  the  outer 
edge  so  as  to  keep  the  felt  always  dry.  The  barrel  is  furnished 
also  with  a  small  propeller,  the  shaft  of  which  runs  inside  of 
the  inner  coil  when  the  latter  is  placed  in  the  barrel.  The 
barrel  is  hung  on  trunnions  by  a  bail  by  which  it  may  be 
raised  for  weighing  on  a  steelyard  supported  on  a  tripod  and 
lifting  lever.  The  steelyard  for  weighing  the  barrel  is  graduated 

*  Trans.  Am.  Soc.  M.  E.  1884. 


526  THE    STEAM-BOILER. 

to  tenths  of  a  pound,  and  a  smaller  steelyard  is  used  for  weigh- 
ing the  coil,  which  is  graduated  to  hundredths  of  a  pound. 

In  operation,  the  coil,  thoroughly  dry  inside  and  out,  is 
carefully  weighed  on  the  small  steelyard.  It  is  then  placed  in 
the  barrel,  which  is  filled  with  cold  water  up  to  the  level  of  the 
top  of  the  globe-valves  of  the  coil  and  just  below  the  level  of  the 
three-way  cock,  the  propeller  being  inserted  and  its  handle  con- 
nected. The  barrel  and  its  contents  are  carefully  weighed  on 
the  large  steelyard ;  the  steam-hose  is  connected  by  means  of 
its  union  to  the  coil,  and  the  three-way  cock  turned  so  as  to  let 
the  steam  flow  through  it  into  the  outer  air,  by  which  means 
the  hose  is  thoroughly  heated  ;  but  no  steam  is  allowed  to  go 
into  the  coil.  The  water  in  the  barrel  is  now  rapidly  stirred  in 
reverse  directions  by  the  propeller  and  its  temperature  taken. 
The  three-way  cock  is  then  quickly  turned,  so  as  to  stop  the 
steam  escaping  into  the  air  and  to  turn  it  into  the  coil ;  the 
thermometer  is  held  in  the  barrel,  and  the  water  stirred  until 
the  thermometer  indicates  from  five  to  ten  degrees  less  than  the 
maximum  temperature  desired.  The  globe-valve  leading  to  the 
coil  is  then  rapidly  and  tightly  closed,  the  three-way  cock  turned 
to  let  the  steam  in  the  hose  escape  into  the  air,  and  the  steam 
entering  the  hose  shut  off.  During  this  time  the  water  is  being 
stirred,  and  the  observer  carefully  notes  the  thermometer  until 
the  maximum  temperature  is  reached,  which  is  recorded  as  the 
final  temperature  of  the  condensing  water.  The  union  is  then 
disconnected  and  the  barrel  and  coil  weighed  together  on  the 
large  steelyard  ;  the  coil  is  then  withdrawn  from  the  barrel  and 
hung  up  to  dry  thoroughly  on  the  outside.  When  dry  it  is 
weighed  on  the  small  scales.  If  the  temperature  of  the  water 
in  the  barrel  is  raised  to  1 10°  or  120°  the  coil  will  dry  to  con- 
stant weight  in  a  few  minutes.  After  the  weight  is  taken,  both 
globe-valves  to  the  coil  are  opened,  the  steam-hose  connected, 
and  all  of  the  condensed  water  blown  out  of  the  coil,  and  steam 
allowed  to  blow  through  the  coil  freely  for  a  few  seconds  at 
full  pressure.  When  the  coil  cools  it  may  be  weighed  again, 
and  is  then  ready  for  another  test. 

If  both  steelyards  were  perfectly  accurate,  and  there  were 
no  losses  by  leakage  or  evaporation,  the  difference  between  the 


STEAM-BOILER    TRIALS.  $2? 

original  and  final  weights  of  the  barrel  and  contents  should  be 
exactly  the  same  as  the  difference  between  the  original  and 
final  weights  of  the  coil.  In  practice  this  is  rarely  found  to  be 
the  case,  since  there  is  a  slight  possible  error  in  each  weighing, 
which  is  larger  in  the  weighing  on  the  large  steelyard.  In 
making  calculations  the  weights  of  the  coil  on  the  small  steel- 
yard should  be  used,  the  weight  on  the  large  steelyard  being 
used  merely  as  a  check  against  large  errors. 

The  late  Mr.  J.  C.  Hoadley  constructed  exceedingly  accu- 
rate apparatus  of  the  "  coil "  type  and  obtained  excellent  re- 
sults. 

It  is  evident  that  this  calorimeter  may  be  used  continuously, 
if  desired,  instead  of  intermittently.  In  this  case  a  continuous 
flow  of  condensing  water  into  and  out  of  the  barrel  must  be 
established,  and  the  temperature  of  inflow  and  outflow  and  of 
the  condensed  steam  read  at  short  intervals  of  time. 

264.  The  Continuous  Calorimeter  is  an  instrument  in 
which  the  operations  of  transfer  of  steam  to  the  instrument 
and  its  examination  are  not  intermitted,  as  is  necessarily  the 
case  in  the  more  commonly  employed  forms  of  the  apparatus. 
The  instrument  being  thus  kept  in  use  continuously,  every 
variation  in  the  quality  of  steam  can  be  observed  and  the  num- 
ber of  observations  can  be  increased  to  any  desired  extent,  and, 
the  apparatus  being  accurate,  any  degree  of  exactness  of  mean 
results  can  be  attained. 

One  of  the  earliest  forms  of  this  instrument  was  devised  by 
Mr.  John  D.  Van  Buren,  of  the  U.  S.  N.  Engineers,  and  In- 
structor in  Engineering  at  the  Naval  Academy,  about  1867. 
This  instrument,  as  constructed  by  Mr.  T.  Skeel,  and  used  by  a 
committee  of  judges*  at  the  exhibition  of  the  American  In- 
stitute, 1874-5,  of  which  the  Author  was  chairman,  was  made 
as  follows  : 

Steam  was  drawn  from  the  steam-drum,  near  the  safety- 
valve,  through  a  felted  pipe  i%  inches  (3.8  cm.)  diameter,  into  a 
rectangular  spiral  or  coil  consisting  of  80  feet  (24.4  m.)  of 
pipe  of  similar  size.  Condensing  water  from  the  street-main 
was  led  into  the  tank  surrounding  the  coil  or  "  worm,"  and 

*  Trans.  Am.  Inst.  1875;  Van  Nostrand's  Mag.  1875. 


528 


THE   STEAM-BOILER. 


issued  at  the  bottom  through  a  "  standard  orifice,"  the  rate  of 
discharge  from  which  had  been  determined  and  the  law  of  its 
variation  with  change  of  head  ascertained.  The  quantity  of 
condensing  water  thus  became  known  by  observing  the  head 
of  water  within  the  tank.  The  water  of  condensation  from  the 
coil  was  caught  in  a  convenient  vessel,  and  weighed  on  scales 
provided  for  that  purpose.  The  temperature  of  the  condensing 
water  at  entrance  and  exit  was  shown  by  fixed  thermometers, 
and  that  of  the  water  of  condensation  at  its  issue  from  the  coil 
was  similarly  shown,  while  the  steam-gauge  placed  on  the  boiler 
gave  the  other  needed  data.  The  calculations  are  evidently 
precisely  the  same  as  with  the  preceding  type  of  calorimeter. 

The  Barrus  Calorimeter*  (Fig.  119)  is  essentially  of  a  small 
surface-condenser.     The  steam  enters  by  the  pipe/.      The  con- 

densing-surface,  a,  is  a  continua- 
tion and  enlargement  of  the 
supply-pipe,  a  i-inch  (2.54  cm.) 
iron  pipe  with  a  length  of  12 
inches  (30.4  cm.)  of  exposed  sur- 
face. This  pipe  is  under  the  full 
pressure  of  steam.  The  con- 
densed water  collects  in  the  lower 
parts  of  the  apparatus,  where  its 
level  is  shown  in  the  glass,  e,  and 
is  drawn  off  by  means  of  the 
valve,  d.  The  injection-water, 
cooled  to  a  temperature  of  40° 
Fahr.,  or  less,  enters  the  wooden 
vessel,  o,  through  the  valve,  b, 
and  circulates  around  the  con- 
densing pipe,  carried  downward 

FIG.  n9.-THE  CONTINUOUS  CALORIMETER.     to    the    bottom     by  means    of  the 

tube  k,  and  overflows  at  the  pipe,  c,  after  passing  through  the 
mixing  chambers,  m.  The  amount  of  water  admitted  is  regu- 
lated so  as  to  secure  a  temperature  at  the  overflow  of  75°  or  80° 
Fahr.,  or  the  approximate  temperature  of  the  surrounding 
atmosphere.  The  thermometers,  f  and  g,  which  are  read  to 


*  Trans.  Am.  Soc.  M.  E.  1884. 


STEAM-BOILER    TRIALS.  S29 

tenths  of  a  degree,  show  the  temperature  of  injection  and  over- 
flow water,  and  the  thermometer,  //,  shows  that  of  the  con- 
densed water.  The  overflow  water  and  the  condensed  water 
are  collected  in  a  system  of  weighing  tanks.  The  steam-pipe 
down  to  the  surface  of  the  water,  and  the  pipes  in  the  lower 
part  of  the  apparatus,  are  covered  with  felt. 

There  is  no  wire-drawing  of  the  steam,  and  no  allowance  to 
be  made  for  specific  heat  of  the  apparatus.  The  only  correc-; 
tion  to  be  made  of  material  amount  is  for  radiation  from  the 
pipes  covered  with  felt,  and  this  can  be  accurately  determined 
by  an  independent  radiation  experiment,  made  when  the  con- 
denser vessel  is  empty. 

Another  form  of  instrument  devised  by  the  same  engineer 
is  arranged  in  such  manner  as  to  permit  the  steam  from  the 
boiler  to  be  dried  and  the  quantity  of  heat  so  employed  meas- 
ured as  a  gauge  of  the  amount  of  water  contained  in  the  steam. 
This  form  of  this  apparatus  is  found  very  satisfactory.* 

The  pipe  conveying  the  steam  to  be  tested  is  usually 
a  half-inch  (1.27  cm.)  iron  pipe.  A  long  thread  is  cut  on  this 
pipe,  and  it  is  screwed  into  the  main  steam  supply-pipe 
of  the  boiler  in  such  a  manner  as  to  extend  diametrically 
across  to  the  opposite  side.  The  inclosed  part  is  perforated 
with  from  40  to  50  small  holes,  and  the  open  end  of  the 
pipe  sealed.  If  the  pipe  is  screwed  into  the  under  side 
the  perforations  begin  at  a  distance  of  one  inch  (2.54  cm.) 
from  the  bottom.  The  connection  is  made  as  short  as 
possible,  and  covered  with  felt.  Where  the  calorimeter  can 
be  attached  to  the  under  side  of  the  main,  the  distance  to 
the  top  valve  need  not  exceed  six  inches  (15  cm.).  In  this 
position  it  is  self-supporting.  The  steam  for  the  superheater 
is  also  supplied  by  a  half-inch  iron  pipe,  but  this  may  be  at- 
tached to  the  main  at  any  convenient  point. 

Steam  to  be  tested  enters  by  the  pipe,  which  has  a 
jacket.  On  passing  out  the  thermometer  gives  its  tem- 
perature, and  it  is  discharged  through  a  small  orifice  -J-  inch 
(0.32  cm.)  in  diameter.  Steam  to  be  superheated  enters 
and  is  superheated  by  a  gas-lamp,  passes  the  thermometer, 

*  Trans.  Am.  Soc.  Mach.  Engrs.,  vol.  vii.  p.  178. 
34 


530 


THE   STEAM-BOILER. 


and  issues  through  an  opening  like  that  for  the  steam.  The 
thermometers  are  immersed  in  oil-wells  surrounded  "by  the 
current  of  steam  to  be  tested,  or  of  that  used  in  drying  the 
boiler-steam. 

In  the  operation  of  this  calorimeter  steam  at  full  pressure 
enters  the  apparatus,  and  the  jacket-steam  is  heated  until 
a  perceptible  rise  of  temperature  above  that  due  the  pres- 
sure indicates  that  its  moisture  has  been  evaporated.  The 
working  having  become  steady,  the  difference  between  the 
temperatures  is  noted  and  corrected  by  deducting  the  ex- 
cess" above  that  of  moist  steam  at  the  observed  pressure, 
and  the  number  of  degrees  of  superheating  thus  determined,  as 
the  rate  of  flow  is  the  same  from  both  orifices.  Here  the 
evaporation  of  one  per  cent  of  moisture  from  steam  at  80 
pounds  pressure  (5.6  kilogs.  per  sq.  cm.)  reduces  the  tempera- 
ture of  superheated  steam  about  iS0./  Fahr.  (io°.4  Cent.), 
and  the  percentage  of  moisture  is  obtained  by  dividing  the 
range  of  superheat,  as  above,  by  this  number,  or  generally  by 
the  quotient  of  the  latent  heat  at  the  observed  pressure  by 
47.5.  The  following  are  data  and  results  obtained  by  the  use 
of  this  apparatus : 

DATA  AND  RESULTS  IN  FULL  OF  CALORIMETER  TESTS. 


rence. 

U 

bo 
U 

is. 

Sfg 

IP 

^   Q. 

Amount  of 
Moisture  in  the 
Wet  Steam. 

*£ 

•OB 

9 

"°  v  2  $ 

<* 

Date 

Gauge- 

T3    £ 

flj  *o 

*,> 

*~  Z  «  S 

v-  c^e 

c* 

£ 

pressure. 

*o  9 

rt 

°  rt 

•o  2 

58 

<u 

1 

fefl 

111 

Hi 

OJ  tfl   O 

•°  •"  •« 

fiili 

<U    (S 
X3  S  r!   1> 

I  sit 

lit 

S5 

* 

* 

2; 

W 

Wo. 

I 

Apr.  13 

89. 

99. 

54-5 

8. 

8. 

9-5 

19 

I.  O2 

2 

14 

89. 

75- 

37- 

5-5 

8. 

9-5 

16. 

0.86 

3 

15 

86. 

74- 

37- 

7- 

10.5 

9-5 

10. 

o  54 

4 

"     16 

86. 

74- 

39- 

9-5 

7- 

9-5 

9- 

0.49 

5 

"     30 

85. 

72. 

38. 

10.5 

8. 

9-5 

6. 

0.32 

6 

May    4 

80. 

77-5 

41-5 

9-5 

8. 

9-5 

9- 

0.49 

7 

5 

84. 

68. 

36.5 

6-5 

7-5 

9-5 

8. 

0-43 

NOTE. — The  duration  of  each  of  these  tests  was  about  one  hour. 


*  Obtained  by  dividing  the  preceding  column  by  18.6,  the  number  of  degrees 
corresponding  to  I  per  cent  of  moisture. 


STEAM-BOILER   TRIALS. 


531 


Many  other  forms  of  calorimeter  have  been  devised,  but 
space  will  not  permit  their  description. 

265.  The  Analysis  of  Gases*  issuing  from  the  furnace 
and  passing  up  the  chimney  is  sometimes  an  important  detail 
of  the  work  of  testing  a  steam-boiler.  Such  an  investigation 
involves  only  an  operation  of  great  simplicity  which  can  easily 
be  performed  by  any  engineer.  If  it  is  not  found  convenient 
to  make  the  analysis  in  the  office  of  the  engineer,  he  can  have 
the  work  done,  at  little  expense,  by  a  chemist  of  known  skill 
and  reliability.  It  is  only  by  a  knowledge  of  the  proportions 
of  constituents  of  the  flue-gases  that  it  can  be  determined 
whether  the  combustion  is  complete,  whether  the  products  of 
combustion  are  diluted  with  excess  of  air,  and  whether  the  fuel 
used  has  been  so  burned  as  to  give  its  best  effect.  Such  analyses 
also  enable  the  engineer  to  ascertain  the  best  method  of  burn- 
ing the  fuel. 

In  sampling  the  gases,  a  matter  in  regard  to  which  some 
precaution     is     advisable,     the 
method  of  Mr.  Hoadley  is  found 
very  satisfactory.! 

Very  great  diversities  in 
composition  often  exist  in  the 
same  flue  at  the  same  time. 
To  obtain  a  sample,  allow  one 
orifice  to  draw  off  flue-gases 
for  each  25  sq.  inches  (161  sq. 
cm.)  of  cross-section  of  flue. 
The  pipes  must  be  of  equal 
diameter  and  of  equal  length. 
These  should  be  secured  in  a 
box  of  galvanized  sheet-iron, 
equal  in  thickness  to  one  course 
of  brick,  so  that  the  ends  may  be  evenly  distributed  over  the 
flue  A  (Fig.  120),  and  their  other  open  ends  inclosed  in  the 


IB; 


FIG.  120. — FLUE-GAS  SAMPLING. 


*  Consult  Handbook  of   Gas  Analysis,  by  C.  Winkler.     London  :     J.   Van 
Voorst.     1885. 


f  Trans.  Am.  Soc.  M.  E.,  vol.  vi. 


532  THE   STEAM-BOILER, 

receiver  B.  If  the  flue  gases  be  drawn  off  from  the  receiver 
B  by  four  tubes  C  C,  into  a  mixing  box  Z>,  beneath,  a  good 
mixture  can  be  obtained. 

The  sampling  of  the  gas  should  be  carried  out  at  intervals 
of  10  to  15  minutes  throughout  the  trial.  The  gas  should  be 
received  in  an  air-tight  pipe  or  jar.  The  composition  of  the 
gases  should  be  determined  as  far  as  regards  carbonic  acid,  car- 
bonic oxide,  and  oxygen.  The  tube  should  be  of  porcelain  or 
glass  for  very  hot  flues,  since  iron  tubes  at  such  temperatures 
are  oxidized.  Supposing  an  analysis  of  the  gas  give  K  per 
cent  of  carbonic  acid,  O  per  cent  of  oxygen,  and  N  per  cent  of 
nitrogen,  then  the  proportion  of  air  actually  used  to  the 
theoretical  quantity  required  is  I  to  x. 


Where 


N  21 

or 


unity  of  weight  of  this  coal  will  then  give,  at  a  temperature  of 
o°  and  a  pressure  of  one  atmosphere, 

1854  ~ 

C  =  carbonic  acid : 

KO 

—-:=  oxygen: 

KN 

—  =  nitrogen. 

The  quantity  of  moisture  in  the  escaping  gases  may  be  cal- 
culated from  the  moisture  in  the  coal,  from  that  formed  by 
burning  the  hydrogen,  and  from  that  contained  in  the  air  ad- 
mitted to  the  furnace  where  the  latter  has  been  determined. 
Any  serious  break  in  the  setting  can  be  detected  by  filling 
the  grate  with  smoky  coal  and  then  closing  the  damper. 

The  apparatus  designed  by  Professor  Elliott,  and  employed 
in  work  carried  on  under  the  direction  of  the  Author,  consists, 


STEAM-BOILER    TRIALS. 


533 


FIG.  i2i.— APPARATUS  FOR 
GAS  ANALYSIS. 


as  shown  in  Fig.  121,  of  two  vertical  glass  tubes,  AB,  A' B' , 
joined  by  rubber-tubing,  E,  at  their  upper 
ends.  The  large  tube,  AB,  is  the  treating, 
the  smaller,  A 'B ',  the  measuring  tube;  the 
1atter  is  suitably  graduated  to  cubic  centi- 
metres. Water-bottles,  K,  L,  are  connected 
with  the  lower  ends  of  the  tubes  by  tubing, 
NO,  N '  O ',  and  are  used  in  effecting  transfer  of 
the  gas  from  tube  to  tube.  M  is  a  funnel 
through  which  the  reagents  used  may  be  in- 
troduced. G,  F,  and  /  are  cocks  of  suitable 
size  and  construction. 

In  filling  the  apparatus  it  is  set  up  conveniently  near  the 
flue,  and  the  line  of  tubing  from  the  collector,  within  the  latter, 
is  connected  with  the  tube  AB.  The  receiver  L  being  de- 
tached the  lower  end  of  AB  is  connected  with  an  aspirator  or 
equivalent  apparatus,  such,  for  example,  as  might  be  improvised 
by  the  use  of  an  air-tight  tank  or  a  barrel ;  and  the  flow  thus 
produced,  when  the  aspirator  is  emptied  of  its  water,  fills  the 
tube  AB  with  gas  drawn  from  the  flue.  It  is  retained  by  clos- 
ing the  valves  F  and  I,  which  had  been  open  during  the  opera- 
tion of  filling.  The  tube  is  then  disconnected  from  the  aspi- 
rator, and  the  receiver,  or  bottle,  L,  connected  as  shown,  and  in 
such  manner  that  no  air  can  reach  the  tube  AB. 

Removing  the  apparatus  to  the  laboratory  or  other  con- 
venient location,  the  analysis  is  made  as  follows : 

Pass  into  A  B'  a  convenient  volume,  as  100  c.c.  of  the  gas, 
and  discharge  the  remainder  through  the  valve  and  funnel  F 
and  M,  filling  the  tube  AB  with  water  from  L.  Transfer  the 
measured  gas  back  to  AB,  through  E,  and  add  a  solution  from 
M,  which  will  absorb  some  one  constituent.  Return  the  gas  to 
A  B' ,  and  again  read  its  volumes.  The  difference  is  the  quan- 
tity of  gas  absorbed.  Repeat  this  process,  using  next  an  ab- 
sorbent which  will  take  up  a  second  constituent  of  the  gas,  and 
thus  obtain  a  second  measure  of  volume ;  and  thus  continue  until 
all  the  desired  determinations  are  made.  All  readings  should 
be  made  at  the  same  temperature,  or  practically  so.  The  tube 


534  THE    STEAM-BOILER. 

AB  should  be  well  washed  at  each  operation,  in  order  that  no 
reagent  should  be  affected  by  traces  of  that  previously  used. 

The  absorbents  employed  are  best  taken  in  the  following- 
order: 

1.  Caustic  potash — to  absorb  carbonic  acid. 

2.  Potassium  pyrogallate — to  absorb  free  oxygen. 

3.  Cuprous  chloride  in  concentrated  hydrochloric-acid  solu- 
tion— to  absorb  carbonic  oxide. 

After  their  use  nitrogen  will  remain,  and  will  be  measured 
as  a  balance  which,  added  to  the  sum  of  the  measured  volumes 
of  gases  absorbed,  should  give  the  original  total.  Where 
weights  are  to  be  determined,  the  volumetric  measures  ob- 
tained as  above  are  to  be  reduced  by  the  usual  process. 

The  atomic  weights  of  the  principal  constituents  being, 
oxygen,  16;  nitrogen,  14;  carbon  monoxide,  28;  carbon  dioxide, 
44,  we  shall  have  by  percentages,  where  the  symbols  represent 
per  cent  in  volumes,  for  each,  when  the  total  is 


M  =  14^+  i6O  +  2SCO  +  44CO,, 


i6O       2SCO       44CO, 

~M>      ~M~>       -^-respectively. 


Since  the  total  per  cent  of  oxygen  is  measured  by  — -  CO,  -f- 

44 

16  12 

~^CO  -f-  ^ee  oxygen,  and  the  total  per  cent  of  carbon  is  — CO9 

28  44 

12 

-| sCO,  we  shall  have  for  the  percentage  of  each, 


28 


32  X  44  X  CO,       16  X  28  X  CO       i6O 

44M  ~  2SM        '  +  M  ' 


_    12  X  44  X  CO,       12  X  28  X  CO 
44M  2SM 


STEAM-BOILER    TRIALS.  535 

or, 


CO,  CO 


The  total  oxygen  is  that  which  entered  the  furnace  as  the 
supporter  of  combustion,  and  is  a  measure  of  the  air  supplied. 
The  ratio  of  free  to  combined  oxygen  is  a  measure  of  the  ratio 
of  the  air  acting  as  a  diluent  simply  to  that  supporting  com- 
bustion. 

Thus  these  measurements  exhibit  the  efficiency  of  combus- 
tion, the  quantity  of  air  employed,  and  the  magnitude  of  the 
wastes  of  heat  at  the  chimney,  occurring  through  imperfect 
combustion  or  excess  of  air-supply.  It  is  evident,  however, 
that  where  moisture  or  steam  accompanies  the  gases,  it  escapes 
measurement ;  this,  however,  introduces  no  important  error  in 
ordinary  work. 

266.  Efficiency  of  Combustion  is  indicated  by  the  analysis 
of  the  flue-gases  with  very  great  certainty.     The  appearance  of 
carbon  monoxide  at  the  chimney  proves  the  combustion  to  be 
imperfect  in   proportion  as  it  is  more  or  less  abundant.     The 
presence  of  unconsumed  oxygen,  on  the  other  hand,  in  the  ab- 
sence   of   carbon    monoxide,  proves   an    excess  of   air-supply. 
Both  gases  appearing  is  a  proof  of  incomplete  intermixture  of 
air  and  combustible,  or  of  so  low  a  temperature  of  furnace  as  to 
check  combustion.     This  analysis  being  compared  with  that  of 
the  fuel  reveals  the   character  and  the  perfection  of  combus- 
tion, and  permits  a  very  exact  determination  to  be  made  of  the 
specific  heat  of  the  gases,  and  is  thus  a  check  on  calculations 
of  wasted  heat. 

267.  Draught-gauges  are  made  for  the  purpose  of  deter- 
mining the  head-producing  draught  and  the  intensity  of  the 
draught,  which  are  of  many  forms,  but  which  usually  depend 
upon  the  measurement  of  the  head  of  water  which  balances 
that  head  at  the  chimney.     A  very  compact  and  accurate  form 


536 


THE   STEAM-BOILER. 


of  draught-gauge,  used  by  the  Author  with  very  satisfactory 
results,  is  that  of  Mr.  J.  M.  Allen  (Fig.  122). 

A  and  A'  are  glass  tubes,  mounted  as  shown,  communicating 
with  each  other  by  a  passage  through  the  base,  which  may  be 
closed  by  means  of  the  stop-cock  shown.  Surrounding  the 
glass  tubes  are  two  brass  rings,  B  and  B '.  These  rings  are 
attached  to  blocks  which  slide  in  dovetailed  grooves  in  the 


FIG.  122. — DRAUGHT-GAUGE. 

body  of  the  instrument,  and  may  be  moved  up  and  down 
by  screws  at  F  F'.  The  scales  are  divided  into  fortieths  of 
an  inch,  and  read  to  thousandths  of  an  inch  by  the  verniers 
e  and  e' ,  which  are  attached  to  the  sliding  rings  B  B ' .  If  the 
two  short  rings  are  set  at  different  heights,  the  difference  in 
readings  will  give  the  difference  of  level.  The  thermometer  is 
for  the  purpose  of  noting  the  temperature  of  the  external  air. 
The  method  of  using  the  instrument  is  as  follows  :*  At  a  con- 

*  The  Locomotive  May,  1884,  p.  67. 


STEAM-BOILER    TRIALS. 


537 


venient  point  near  the  base  of  the  chimney  a  hole  is  made 
large  enough  to  insert  a  thermometer.  The  height  from  this 
opening  to  the  top  of  chimney,  and  also  of  grates,  should  be 
noted.  The  chimney-gauge  is  attached  to  some  convenient 
wall.  The  tubes  are  filled  about  half  full  of  water,  when  the 
verniers  afford  an  easy  means  of  setting  it  perpendicular.  One 
end  of  a  flexible  rubber  tube  is  then  inserted  into  the  upper 
end  of  one  of  the  glass  tubes,  and  the  other  end  of  the  tube  is 
in  the  chimney-flue.  The  tubes  B  B'  are  adjusted  until  their 
upper  ends  are  just  tangent  to  the  surface  of  the  water  in  the 
two  tubes.  The  reading  of  the  two  scales  is  then  taken,  and 
their  difference.  At  the  same  time  the  temperature  of  the 
flue  is  noted,  as  well  as  that  of  the  external  atmosphere.  Com- 
parison may  then  be  made  with  the  following  table,  computed 
for  use  in  this  connection  for  a  chimney  100  feet  high,  with 
various  temperatures  outside  and  inside  of  the  flue,  and  on  the 
supposition  that  the  temperature  of  tJie  chimney  is  uniform 
from  top  to  bottom — an  inaccurate  though  usual  assumption, 
however.  For  other  heights  than  100  feet,  the  theoretical 
height  is  found  by  simple  proportion,  thus :  Suppose  the  exter- 
nal temperature  is  60°,  temperature  of  flue  380°,  height  of 
chimney  137  feet,  then  under  60°  at  the  top  of  the  table,  and 
opposite  to  380°  interpolated  in  the  left-hand  margin,  we 
find  .52". 

Then    100  :  137  ::  .52"  :  .71",  which  is  the   required  height 
for  a  137-foot  chimney,  and  similarly  for  any  other  height. 


HEIGHT  OF  WATER  COLUMN  DUE  TO  UNBALANCED    PRESSURE   IN 
CHIMNEY   100  FEET  HIGH. 


Temperature 

TEMPERATURE  (FAHR.)  OF  THE  EXTERNAL  AIR  —  BAROMETER,  14.7. 

in  the 

Chimney. 

Fahr. 

2O° 

40° 

6O° 

80° 

1OO- 

22O 

.419 

•  355 

.298 

.244 

.192 

250 

.468 

.405 

•347 

.294 

.242 

300 

•541 

.478 

.420 

.367 

•  315 

350 

.607 

•543 

.486 

•432 

.380 

400 

.662 

.598 

•  541 

.488 

•  436 

450 

.714 

.651 

•593 

•540 

.488 

500 

.760 

.697 

•  639 

.586 

•534 

CHAPTER  XV. 

STEAM-BOILER   EXPLOSIONS.* 

268.  Steam-boiler  Explosions  are  among  the  most  terrible 
and  disastrous  of  all  the  many  kinds  of  accident,  the  introduc- 
tion of  which  has  marked  the  advancement  of  civilization  and 
its  material  progress.  Introduced  by  Captain  Savery  at  the 
beginning  of  the  i8th  century  with  the  first  attempts  to  apply 
steam-power  to  useful  purposes,  they  have  increased  in  fre- 
quency and  in  their  destructiveness  of  life  and  property  con- 
tinually, with  increasing  steam-pressures  and  the  unintermitted 
growth  of  these  magazines  of  stored  energy,  until  to-day  the 
amount  of  available  energy  so  held  in  control,  and  liable  at 
times  to  break  loose,  is  often  as  much  as  two  or  even  three 
millions  of  foot-pounds  (276,500  to  414,760  kilogrammetres), 
and  sufficient  to  raise  the  enclosing  vessel  10,000  or  even  20,000 
feet  (3048  to  6096  m.)  into  the  air,  the  fluid  having  a  total 
energy,  pound  for  pound,  only  comparable  with  that  of  gun- 
powder. 

In  this  and  the  following  article  it  is  proposed  to  present 
the  results  of  a  series  of  calculations  relating  to  the  magnitude 
of  the  available  energy  contained  in  masses  of  steam  and  of 
water  in  steam-boilers.  This  energy  has  been  seen  to  be  meas- 
ured by  the  amount  of  work  which  may  be  obtained  by  the 
gradual  reduction  of  the  temperature  of  the  mass  to  that  due 
atmospheric  pressure  by  continuous  expansion. 

The  subject  is  one  which  has  often  attracted  the  attention 
of  both  the  man  of  science  and  the  engineer.  Its  importance, 
both  from  the  standpoint  of  pure  science  and  from  that  of 
science  applied  in  engineering  and  the  minor  arts,  is  such  as 

*  This  chapter  has  been  separately  printed  with  slight  modifications  as  a 
monograph  "On  Steam-boiler  Explosions,"  and  published  by  the  Messrs. 
Wiley. 


STEAM-BOILER  EXPLOSIONS.  539 

would  justify  the  expenditure  of  vastly  more  time  and  atten- 
tion than  has  yet  ever  been  given  it.  Mr.  Airy  *  and  Professor 
Rankinef  published  papers  on  this  subject  in  the  same  number 
of  the  Philosophical  Magazine  (Nov.  1863),  the  one  dated  the 
3d  September  and  the  other  the  5th  October  of  that  year. 
The  former  had  already  presented  an  abstract  of  his  work  at  the 
meeting  of  the  British  Association  of  that  year. 

In  the  first  of  these  papers  it  is  remarked  that  "  very  little 
of  the  destructive  effect  of  an  explosion  is  due  to  the  steam 
which  is  confined  in  the  steam-chamber  at  the  moment  of  the 
explosion.  The  rupture  of  the  boiler  is  due  to  the  expansive 
power  common  at  the  moment  to  the  steam  and  the  water,  both 
at  a  temperature  higher  than  the  boiling-point ;  but  as  soon  as 
the  steam  escapes,  and  thereby  diminishes  the  compressive 
force  upon  the  water,  a  new  issue  of  steam  takes  place  from  the 
water,  reducing  its  temperature  ;  when  this  escapes,  and  further 
diminishes  the  compressive  force,  another  issue  of  steam  of 
lower  elastic  force  from  the  water  takes  place,  again  reducing 
its  temperature  :  and  so  on,  till  at  length  the  temperature  of 
the  water  is  reduced  to  the  atmospheric  boiling-point,  and  the 
pressure  of  the  steam  (or  rather  the  excess  of  steam-pressure 
over  atmospheric  pressure)  is  reduced  to  o." 

Thus  it  is  shown  that  it  is  the  enormous  quantity  of  steam 
so  produced  from  the  water,  during  this  continuous  but  exceed- 
ingly rapid  operation,  that  produces  the  destructive  effect  of 
steam-boiler  explosions.  The  action  of  the  steam  which  may 
happen  to  be  present  in  the  steam-space  at  the  instant  of  rupture 
is  considered  unimportant. 

Mr.  Airy  had,  as  early  as  1849,  endeavored  to  determine  the 
magnitude  of  the  effect  thus  capable  of  being  produced,  but  had 
been  unable  to  do  so  in  consequence  of  deficiency  of  data.  His 
determinations,  as  published  finally,  were  made  at  his  request  by 
Professor  W.  H.  Miller.  The  data  used  are  the  results  of  the  ex- 
periments of  Regnault  and  of  Fairbairn  and  Tate  on  the  relations 
of  pressure,  volume,  and  temperature  of  steam,  and  of  an  experi- 

*  "  Numerical   Expression  of    the  Destructive  Energy  in  the  Explosions  of 
Steam-boilers." 

f  "  On  the  Expansive  Energy  of  Heated  Water." 


54°  THE   STEAM-BOILER. 

ment  by  Mr.  George  Biddle,  by  which  it  was  found  that  a  locomo- 
tive boiler,~at  four  atmospheres  pressure,  discharged  one  eighth 
of  its  liquid  contents  by  the  process  of  continuous  vaporization 
above  outlined,  when,  the  fire  being  removed,  the  pressure  was 
reduced  to  that  of  the  atmosphere.  The  process  of  calculation 
assumes  the  steam  so  formed  to  be  applied  to  do  work  expand- 
ing down  to  the  boiling-point,  in  the  operation.  The  work  so 
done  is  compared  with  that  of  exploding  gunpowder,  and  the 
conclusion  finally  reached  is  that  "  the  destructive  energy  of  one 
cubic  foot  of  water,  at  a  temperature  which  produces  the  pres- 
sure of  60  Ibs.  to  the  square  inch,  is  equal  to  that  of  one  pound 
of  gunpowder." 

The  work  of  Rankine  is  more  exact  and  more  complete,  as 
well  as  of  greater  practical  utility.  The  method  adopted  is  that 
to  be  described  presently,  and  involves  the  application  of  the 
formulas  for  the  transformation  of  heat  into  work  which  had 
been  ten  years  earlier  derived  by  Rankine  and  by  Clausius,  inde- 
pendently. This  paper  would  seem  to  have  been  brought  out 
by  the  suggestion  made  by  Airy  at  the  meeting  of  the  British 
Association.  Rankine  shows  that  the  energy  developed  during 
this,  which  is  an  adiabatic  method  of  expansion,  depends  solely 
upon  the  specific  heat  and  the  temperatures  at  the  beginning 
and  the  end  of  the  expansion,  and  has  no  dependence,  in  any 
manner,  upon  any  other  physical  properties  of  the  liquid.  He 
then  shows  how  the  quantity  of  energy  latent  in  heated  water 
may  be  calculated,  and  gives,  in  illustration,  the  amount  so  de- 
termined for  eight  temperatures  exceeding  the  boiling-point. 

This  subject  attracted  the  attention  of  the  engineer  at  a  very 
early  date.  Familiarity  with  the  destructive  effects  of  steam- 
boiler  explosions,  the  singular  mystery  that  has  been  supposed 
to  surround  their  causes,  the  frequent  calls  made  upon  him,  in 
the  course  of  professional  practice  and  of  his  studies,  to  exam- 
ine the  subject  and  to  give  advice  in  matters  relating  to  the  use 
of  steam,  and  many  other  hardly  less  controlling  circumstances, 
invest  this  matter  with  an  extraordinary  interest. 

A  steam-boiler  is  a  vessel  in  which  is  confined  a  mass  of 
water,  and  of  steam,  at  a  high  temperature,  and  at  a  pressure 
greatly  in  excess  of  that  of  the  surrounding  atmosphere.  The 


STEAM-BOILER   EXPLOSIONS.  541 

sudden  expansion  of  this  mass  from  its  initial  pressure  down  to 
that  of  the  external  air,  occurring  against  the  resistance  of  its 
"  shell "  or  other  masses  of  matter,  may  develop  a  very  great 
amount  of  work  by  the  transformation  of  its  heat  into  mechani- 
cal energy,  and  may  cause,  as  daily  occurring  accidents  remind 
us,  an  enormous  destruction  of  life  and  property.  The  enclosed 
fluid  consists,  in  most  cases,  of  a  small  weight  ,of  steam  and  a 
great  weight  of  water.  In  a  boiler  of  a  once  common  and  still 
not  uncommon  marine  type,  the  Author  found  the  weight  of 
steam  to  be  less  than  2  50  pounds,  while  the  weight  of  water  was 
nearly  40,000  pounds.  As  will  be  seen  later,  under  such  con- 
ditions, the  quantity  of  energy  stored  in  the  water  is  vastly  in 
excess  of  that  contained  in  the  steam,  notwithstanding  the  fact 
that  the  amount  of  energy  per  unit  of  weight  of  fluid  is  enor- 
mously the  greater  in  the  steam.  A  pound  of  steam,  at  a  pres- 
sure of  six  atmospheres  (88.2  pounds  per  square  inch),  above 
zero  of  pressure,  and  at  its  normal  temperature,  177  C.  (319°  F.), 
has  stored  in  it  about  75  British  thermal  units  (32  calories), 
or  nearly  70,000  foot-pounds  of  mechanical  energy  per  unit  of 
weight,  in  excess  of  that  which  it  contains  after  expansion  to 
atmospheric  pressure.  A  pound  of  water  accompanying  that 
steam,  and  at  the  same  pressure,  has  stored  within  it  but  about 
one  tenth  as  much  available  energy.  Nevertheless,  the  dispro- 
portion of  weight  of  the  two  fluids  is  so  much  greater  as  to  make 
the  quantity  of  energy  stored  in  the  steam  contained  in  the 
boiler  quite  insignificant  in  comparison  with  that  contained  in 
the  water.  These  facts  have  been  fully  illustrated  by  the  figures 
presented  already. 

269.  The  Energy  Stored  in  steam-boilers  is  capable  of 
very  exact  computation  by  the  methods  already  described,  and 
the  application  of  the  results  there  reached  gives  figures  that 
are  quite  sufficient  to  account  for  the  most  violently  destruc- 
tive of  all  recorded  cases  of  explosion. 

A  steam-boiler  is  not  only  an  apparatus  by  means  of  which 
the  potential  energy  of  chemical  affinity  is  rendered  actual 
and  available,  but  it  is  also  a  storage-reservoir,  or  a  magazine, 
in  which  a  quantity  of  such  energy  is  temporarily  held  ;  and 
this  quantity,  always  enormous,  is  directly  proportional  to  the 


542  THE    STEAM-BOILER. 

weight  of  water  and  of  steam  which  the  boiler  at  the  time  con- 
tains. 

Comparing  the  energy  of  water  and  of  steam  in  the  steam- 
boiler  with  that  of  gunpowder,  as  used  in  ordnance,  it  has  been 
found  that  at  high  pressures  the  former  become  possible  rivals 
of  the  latter.  The  energy  of  gunpowder  is  somewhat  variable, 
but  it  has  been  seen  that  a  cubic  foot  of  heated  water,  under  a 
pressure  of  60  or  70  pounds  per  square  inch,  has  about  the  same 
energy  as  one  pound  of  gunpowder.  The  gunpowder  exploded 
has  energy  sufficient  to  raise  its  own  weight  to  a  height  of  nearly 
50  miles,  while  the  water  has  enough  to  raise  its  weight  about 
one  sixtieth  that  height.  At  a  low  red  heat  water  has  about 
40  times  this  latter  amount  of  energy  in  a  form  to  be  so  ex- 
pended. Steam,  at  4  atmospheres  pressure,  yields  about  one 
third  the  energy  of  an  equal  weight  of  gunpowder.  At  7  at- 
mospheres it  has  as  much  energy  as  two  fifths  of  its  own  weight 
of  powder,  and  at  higher  pressures  its  energy  increases  very 
slowly. 

.  Below  are  presented  the  weights  of  steam  and  of  water  con- 
tained in  each  of  the  more  common  forms  of  steam-boilers,  the 
total  and  relative.amounts  of  energy  confined  in  each  under  the 
usual  conditions  of  working  in  every-day  practice,  and  their 
relative  destructive  power  in  case  of  explosion. 

In  illustration  of  the  results  of  application  of  the  computa- 
tions which  have  been  given  in  §  142,  and  for  the  purpose  of 
obtaining  some  idea  of  the  amount  of  destructive  energy  stored 
in  steam-boilers  of  familiar  forms,  such  as  the  engineer  is  con- 
stantly called  upon  to  deal  with,  and  such  as  the  public  are 
continually  endangered  by,  the  following  table  has  been  calcu- 
lated. This  table  is  made  up  by  Mr.  C.  A.  Carr,  U.  S.  N., 
from  notes  of  dimensions  of  boilers  designed  or  managed  at 
various  times  by  the  Author,  or  in  other  ways  having  special 
interest  to  him.  They  include  nearly  all  of  the  forms  in  com- 
mon use,  and  are  representative  of  familiar  and  ordinary  prac- 
tice. 

No.  I  is  the  common,  simple,  plain  cylindrical  boiler.  It  is 
often  adopted  when  the  cheapness  of  fuel  or  the  impurity  of 
the  water  supply  renders  it  unadvisable  to  use  the  more  com- 


STEAM-BOILER  EXPLOSIONS. 


543 


omO 
^CNro 


m       in     O      ro 


in     O 
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ovOM  10 
Tt-i-irc  <N 
io^'^-  co 


Tf-COOO 


voco 
OH 


tt<   0 


jn  . 

£  in    M"   \o" 


Hco^t^ 

fL,Ov-<i-<Nm 


M,  ° 


"  t  ?  o  s; 


n'! 


oo 
inm 

o"    <N" 


moo 
i^ot^ 

"  " 


ro    cT   oo"       H" 

int~»o        co 


ooo 
t-^ot-, 

in  vo"   vo" 
mvo-j- 


O-^-'^'l-i 

vovovotx 


N          Wt^ 

O        t^w 


voMvo 


c> 


ro       in   oo      ro 


-<j-MO 
VOt^-^- 
t^'*00 
intivo" 


oo'in 


'd'H 


OOO 
mtnm 

CV!<S<N 


•HDNJ  aavnog  aaj 
aanssaaj; 


o          O        2 

CO  ro         Q 


-O 
^t^ 

oo 


O'*        mvo 
i-i        N  in       O 

H.      ro       t^     oo^ 


CT'invO 

y)        wco 


OOO 

t~-O 


3  3 


c       o  o 


2  «2  «» 
« 


544  THE   STEAM-BOILER. 

plex,  though  more  efficient,  kinds.  It  is  the  cheapest  and 
simplest  in  form  of  all  the  boilers.  The  boiler  here  taken  was 
designed  by  the  Author  many  years  ago  for  a  mill  so  situated 
as  to  make  this  the  best  form  for  adoption,  and  for  the  reasons 
above  given.  It  is  thirty  inches  in  diameter,  thirty  feet  long, 
and  is  rated  at  ten  H.  P.,  although  such  a  boiler  is  often  forced 
up  to  double  that  capacity.  The  boiler  weighs  a  little  over  a 
ton,  and  contains  more  than  twice  its  weight  of  water.  The 
water,  at  a  temperature  corresponding  to  that  of  steam  at  100 
pounds  pressure  per  square  inch,  contains  over  46,600,000  foot- 
pounds of  available  explosive  energy,  while  the  steam,  which 
has  but  one  fifth  of  one  per  cent  of  the  weight  of  the  water, 
stores  about  700,000  foot-pounds,  giving  a  total  of  47,000,000 
foot-pounds,  nearly,  or  sufficient  to  raise  one  pound  nearly 
10,000  miles.  This  is  sufficient  to  throw  the  boiler  19,000  feet 
high,  or  nearly  four  miles,  and  with  an  initial  velocity  of  pro- 
jection of  noo  feet  per  second. 

Comparing  this  with  the  succeeding  cases,  it  is  seen  that 
this  is  the  most  destructive  form  of  boiler  on  the  whole  list. 
Its  simplicity  and  its  strength  of  form  make  it  an  exceedingly 
safe  boiler,  so  long  as  it  is  kept  in  good  order  and  properly 
managed;  but  if,  through  phenomenal  ignorance  or  reckless- 
ness on  the  part  of  proprietor  or  attendant,  the  boiler  is  ex- 
ploded, the  consequences  are  usually  exceptionally  disastrous. 

No.  2  was  a  "  Cornish"  boiler  designed  by  the  Author,  about 
1860,  and  set  to  be  fired  under  the  shell.  It  was  6  feet  by  36, 
and  contained  a  36-inch  flue.  The  shell  and  flue  were  both  of 
iron  f  inch  in  thickness.  The  boiler  was  tested  up  to  60 
pounds,  at  which  pressure  the  flue  showed  some  indications  of 
alteration  of  form.  It  was  strengthened  by  stay-rings,  and  the 
boiler  was  worked  at  30  pounds.  The  boiler  contained  about 
12  tons  of  water,  weighed  itself  7^  tons,  and  the  volume  of 
steam  in  its  steam-space  weighed  but  31^  pounds.  The  stored 
available  energies  were  about  57,600,000  foot-pounds,  and  about 
700,000  of  foot-pounds  in  the  water  and  steam,  respectively,  a 
total  of  nearly  60,000,000.  This  was  sufficient  to  throw  the 
boiler  to  the  height  of  3400  feet,  or  over  three  fifths  of  a  mile. 

Comparing  this  with  the  preceding,  it  is  seen  that  the  intro- 


STEAM-BOILER   EXPLOSIONS.  545 

duction  of  the  single  flue,  of  half  the  diameter  of  the  boiler, 
and  the  reduced  pressure,  have  reduced  the  relative  destructive 
power  to  but  little  more  than  one  sixth  that  of  the  preceding 
form. 

No.  3  is  a  "two-flue"  or  Lancashire  boiler,  similar  in  form 
and  in  proportions  to  many  in  use  on  the  steamboats  plying  on 
our  Western  rivers,  and  which  have  acquired  a  very  unenviable 
reputation  by  their  occasional  display  of  energy  when  carelessly 
handled.  That  here  taken  in  illustration  was  designed  by  the 
Author.  42  inches  in  diameter,  with  two  i4~inch  flues  of  f  iron, 
and  is  here  taken  as  working  at  a  pressure,  as  permitted  by'law^ 
of  150  pounds  per  square  inch.  It  is  rated  at  35  horse-power, 
but  such  a  boiler  is  often  driven  far  above  this  figure.  The 
boiler  contains  about  its  own  weight  (3  tons)  of  water,  and  but 
37  pounds  of  steam.  The  stored  available  energy  is  83,000,000 
foot-pounds,  of  which  the  steam  contains  but  a  little  above  five 
per  cent.  Its  explosion  would  uncage  sufficient  energy  to  throw 
the  boiler  nearly  2^-  miles  high,  with  an  initial  velocity  of  900 
feet  per  second.  Both  this  boiler  and  the  plain  cylinder  are 
thus  seen  to  have  a  projectile  effect  only  to  be  compared  to 
that  of  ordnance. 

No.  4  is  the  common  plain  tubular  boiler,  substantially  as 
designed  by  the  Author  at  about  the  same  time  with  those  al- 
ready described.  It  is  a  favorite  form  of  boiler,  and  deserv- 
edly so,  with  all  makers  and  users  of  shell-boilers.  That  here 
taken  is  60  inches  in  diameter,  containing  66  3-inch  tubes,  and 
is  15  feet  long.  The  specimen  here  chosen  has  850  feet  of 
heating  and  30  feet  of  grate-surface,  is  rated  at  60  horse-power, 
but  is  oftener  driven  up  to  75,  weighs  9500  pounds,  and  contains 
nearly  its  own  weight  of  water,  but  only  21  pounds  of  steam, 
when  under  a  pressure  of  75  pounds  per  square  inch,  which  is 
below  its  safe  allowance.  It  stores  51,000,000  foot-pounds  of 
energy,  of  which  but  4  per  cent  is  in  the  steam,  and  this  is 
enough  to  drive  the  boiler  just  about  one  mile  into  the  air, 
with  an  initial  velocity  of  nearly  600  feet  per  second.  The 
common  upright  tubular  boiler  may  be  classed  with  No.  4. 

Nos.  5-8  are  locomotive   boilers,  of  which  drawings  and 

35 


54-6  THE    STEAM-BOILER. 

weights  were  furnished  by  the  builders.  They  are  of  different 
sizes,  and  both  freight  and  passenger  engines.  The  powers  are 
probably  rated  low.  They  range  from  1 5  to  50  square  feet  in  area 
of  grate,  and  from  £75  to  1350  square  feet  of  heating-surface. 
In  weight  the  range  is  much  less,  running  from  2^  to  a  little 
above  3  tons  of  water,  and  from  20  to  30  pounds  of  steam,  as- 
suming all  to  carry  125  pounds  pressure^  The  boilers  are  seen 
to  weigh  from  2-J  to  3  times  as  much  as  the  water.  These  pro- 
portions differ  considerably  from  those  of  the  stationary  boilers 
which  have  been  already  considered.  The  stored  energy  aver- 
ages about  70,000,000  foot-pounds,  and  the  heights  and  veloci- 
ties of  projection  not  far  from  3000  and  500  feet ;  although 
in  one  case  they  became  nearly  one  mile  and  550  feet,  respec- 
tively. The  total  energy  is  only  exceeded,  among  the  stationary 
boilers,  by  the  two-flued  boiler  at  150  pounds  pressure. 

Nos.  9  and  10  are  marine  boilers  of  the  Scotch  or  "drum" 
form.  These  boilers  have  come  into  use  by  the  usual  pu.  less 
of  selection,  with  the  gradual  increase  of  steam-pressures  oc- 
curring during  the  past  generation  as  an  accompaniment  of  the 
introduction  of  the  compound  engine  and  high  ratios  of  expan- 
sion. The  selected  examples  are  designed  for  use  in  the 
new  vessels  of  the  U.  S.  Navy.  The  dimensions  are  obtained 
from  the  Navy  Department,  as  figured  by  the  Chief  Draughts- 
man, Mr.  Geo.  B.  Whiting.  The  first  is  that  designed  for  the 
Nipsic,  the  second  for  the  Despatch.  They  are  of  300  and 
350  horse-power,  and  contain,  respectively,  73,000,000  and 
110,000,000  of  foot-pounds  of  available  energy,  or  about  3000 
foot-pounds  per  pound  of  boiler,  and  sufficient  to  give  a  height 
and  velocity  of  projection  of  3000  and  above  400  feet.  These 
boilers  are  worked  at  a  lower  pressure  than  locomotive  boilers ; 
but  the  pressure  is  gradually  and  constantly  increasing  from 
decade  to  decade,  and  the  amount  of  explosive  energy  carried 
in  our  modern-steam  vessels  is  now  enormously  greater  than 
that  of  our  locomotives,  and  in  some  cases  already  considerably 
exceeds  that  which  they  would  carry  were  they  supplied  with 
boilers  of  the  locomotive  type  and  worked  at  locomotive  pres- 
sures. The  explosion  of  the  locomotive  boiler  endangers  com- 


STE4M-&OILER  EXPLOSIONS.  547 

paratively  few  lives,  and  seldom  does  serious  injury  to  property 
outside  the  engine  itself.  The  explosion  of  one  of  these  marine 
boilers  while  at  sea  would  be  likely  to  be  destructive  of  many 
lives,  if  not  of  the  vessel  itself  and  all  on  board. 

Nos.  II  and  12  are  boilers  of  the  older  types,  such  as  are 
still  to  be  seen  in  steamboats  plying  upon  the  Hudson  and 
other  of  our  rivers,  and  in  New  York  harbor  and  bay.  No.  1 1 
is  a  return-tubular  boiler  having  a  shell  10  feet  in  diameter  by 
23  feet  long,  2  furnaces  each  7f  feet  deep,  8  1 5-inch  and  2  9-inch 
flues,  and  85  return-tubes,  4^  inches  by  15  feet.  The  boiler 
weighs  25  tons,  contains  nearly  2.0  tons  of  water  and  70  pounds 
of  steam,  and  at  30  pounds  pressure  stores  92,000,000  foot- 
pounds of  available  energy,  of  which  2-J-  per  cent  resides  in  the 
steam.  This  is  enough  to  hoist  the  boiler  one  third  of  a  mile 
with  a  velocity  of  projection  of  330  feet  per  second.  The 
second  of  these  two  boilers  is  of  the  same  weight,  also  of  about 
200  horse-power,  but  carries  a  little  more  water  and  steam  and 
stores  104,000,000  foot-pounds  of  energy,  or  enough  to  raise  it 
1900  feet.  This  was  a  return-flue  boiler,  33  feet  long  and  hav- 
ing a  shell  8f  feet  in  diameter,  flues  8^  to  15  inches  in  diameter, 
according  to  location. 

The  "  sectional  "  boilers  are  here  seen  to  have,  for  250  horse- 
power each,  weights  ranging  from  about  35,000  to  55,000 
pounds,  to  contain  from  15,000  to  30,000  pounds  of  water  and 
from  25  to  58  pounds  of  steam,  to  store  from  1 10,000,000  to 
230,000,000  foot-pounds  of  energy,  equal  to  from  2000  to  5000 
foot-pounds  per  pound  of  boiler.  The  stored  available  energy 
is  thus  usually  less  than  that  of  any  of  the  other  stationary 
boilers,  and  not  very  far  from  the  amount  stored,  pound  for 
pound,  by  the  plain  tubular  boiler,  the  best  of  the  older  forms. 
It  is  evident  that  their  admitted  safety  from  destructive  explo- 
sion does  not  come  from  this  relation,  however,  but  from  the 
division  of  the  contents  into  small  portions,  and  especially  from 
those  details  of  construction  which  make  it  tolerably  certain 
that  any  rupture  shall  be  local.  A  violent  explosion  can  only 
come  of  the  general  disruption  of  a  boiler  and  the  liberation  at 
once  of  large  masses  of  steam  and  water. 


548 


THE   STEAM-BOILER. 


270.  The  Energy  of  Steam  alone,  as  stored  in  the  boiler, 
is  given  by  column  10  of  the  preceding  table.  It  has  been  seen 
that  it  forms  but  a  small  and  unimportant  fraction  of  the  total 
stored  energy  of  the  boiler.  The  next  table  exhibits  the  effect 
of  this  portion  of  the  total  energy,  if  considered  as  acting  alone. 


STORED  ENERGY   IN  THE   STEAM-SPACE  OF  BOILERS. 


TYPE. 

Total  Energy. 

Stored  in 
Steam 
(ft.-lbs.) 
per  Ib.  of 
Boiler. 

Height  of 
Projection. 

Initial 
Velocity 
per  second. 

I     Plain  Cylinder       .        .  . 

] 

676,693 
709,310 

J.377-357 
,022.731 
,483.896 
,135,802 
,766,447 
302.431 
462  430 
,316,392 
.570,517 
.643-854 
j,  108,110 
5.513,830 
,311-377 

271 
42 

351 

108 
76 
85 
86 
107 

54 
61 

28 

29 
61 

79 
24 

27I  f 
42 
351 

108 
76 

85 
86 
107 

K 

28 
29 
61 

79 
24 

t. 

132  f 
32 
150 
83 
69 
74 
74 
83 
59 
62 
42 
43 
59 
7i 
39 

t. 

2.   Cornish  

3.  Two-flue  Cylinder  

4    Plain  Tubular 

5    Locomotive      .            . 

6              "           

7.              " 

«.              "            

Q    Scotch  Marine 

10              " 

ii     Flue  and  Return-tube   

12                                                            ..,'..... 

13    Water-tube 

M" 

je.                 " 

The  study  of  this  table  is  exceedingly  interesting,  if  made 
with  comparison  of  the  figures  already  given,  and  with  the  facts 
stated  above.  It  is  seen  that  the  height  of  projection,  by  the 
action  of  steam  alone,  under  the  most  favorable  circumstances, 
is  not  only  small,  insignificant  indeed,  in  comparison  with  the 
height  due  the  total  stored  energy  of  the  boiler,  but  is  proba- 
bly entirely  too  small  to  account  for  the  terrific  results  of  ex- 
plosions frequently  taking  place.  The  figures  are  those  for  the 
stored  energy  of  steam  in  the  working  boiler  ;  they  may  be 
doubled,  or  even  trebled,  for  cases  of  low  water;  they  still 
remain,  however,  comparatively  insignificant. 

The  enormous  power  of  molecular  forces,  even  when  heat 
is  not  added  to  reinforce  them,  is  illustrated  by  the  often  de- 


STEAM-BOILER   EXPLOSIONS. 


549 


scribed  experiments  of  an  artillery  officer  at  Quebec*  and  others 
in  which  a  large  bombshell  is  filled 
with  water,  safely  plugged,  and 
exposed  to  low  temperature.  In 
such  cases  the  expansive  force  ex- 
erted, when  freezing,  by  the  for- 
mation of  ice  and  the  increase  of 
volume  accompanying  the  forma- 
tion of  the  crystals,  either  drives 
out  the  plug,  sometimes  project- 
ing it  hundreds  of  yards  (Fig. 
123),  or  actually  bursts  the  thick  iron  case. 

In  the  more  familiar  cases  of  purposely  produced  explosion, 
the  expansion  is  caused  by  the  production  of  great  quantities 
of  gas  previously  in  solid  form.  The  violence  of  the  familiar 
explosives  as  used  in  ordnance,  in  mining  operations,  is  com- 


FIG.  123. — EXPANSIVE  FORCE  OF  ICE. 


FIG.  124.— AN  EXPLOSION. 

monly  due  to  this  combined  effect  of  heat  and  chemical  action, 
occurring  by  the  sudden  action  of  powerful  forces.  In  the 
steam-boiler  explosion  mighty  forces  previously  long  held  in 
subjection  finally  overcome  all  resistance,  and  their  sudden  ap- 
plication to  external  bodies  constitutes  the  disaster. 

271.  Explosion  and  Bursting  are  terms  which,  as  often  tech- 
nically used  by  the  engineer,  represent  radically  different  phe- 
nomena. The  explosion  of  a  steam-boiler  is  a  sudden  and  violent 

*  Phenomena  of  Heat.     Cazin. 


550  THE   STEAM-BOILER. 

disruption,  permitting  the  stored  heat-energy  of  the  enclosed 
water  and  steam  to  be  expended  in  the  enormously  rapid  ex- 
pansion of  its  own  mass,  and,  often,  in  the  projection  of  parts 
of  the  boiler  in  various  directions,  with  such  tremendous  power 
as  to  cause  as  great  destruction  of  life  and  property  as  if  the 
explosion  were  that  of  a  powder-magazine.  The  bursting  of  a 
boiler  is  commonly  taken  to  be  the  rupture,  locally,  of  the 
structure,  by  the  yielding  of  its  weakest  part  to  a  pressure 
which  at  the  moment  may  not  be  deemed  excessive,  but  which 
is  too  great  for  the  weakened  spot.  The  collapse  of  a  flue  is  a 
form  of  rupture  which  is  ordinarily  considered  as  of  the  second 
class.  With  high  steam-pressure,  bursting  or  the  collapse  of  a 
flue  may  occur  with  a  loud  report,  and  may  even  cause  some 
di'splacement  of  the  boiler  ;  but  it  is  not  generally  termed  an 
explosion  when  the  boiler  is  simply  ruptured,  and  is  not  torn 
into  separated  pieces.  There  is,  however,  no  real  boundary, 
and  the  one  grades  into  the  other,  with  no  defined  line  of  de- 
marcation. 

It  occasionally  happens  that  an  explosion  takes  place  with 
such  extraordinary  violence  and  destructive  effect  that  it  has 
been  thought  best,  especially  by  French  writers,  to  class  it  by 
itself,  and  it  is  denoted  a  detonant  or  fulminant  explosion, 
"  explosion  fulminant e"  In  such  cases  the  report  is  like  that 
of  an  enormous  piece  of  ordnance  ;  the  boiler  is  often  rent  into 
many  parts,  or  even  completely  broken  up,  as  if  by  dynamite ; 
and  surrounding  objects  are  destroyed  as  if  by  the  discharge  of 
a  park  of  artillery. 

In  any  steam-boiler  there  may  at  any  time  exist  a  state 
of  equilibrium  between  the  resisting  power  of  the  boiler  and 
the  steam -pressure.  In  ordinary  working,  the  latter  is  far 
within  the  former ;  but  as  time  passes  the  limiting  condition 
is  gradually  approached,  and  in  every  explosion  the  line  is 
passed.  The  pressure  may  rise  until  the  limit  of  strength  is  at- 
tained, or  the  resisting  power  of  the  boiler  may  decrease  to  the 
limit :  in  either  case  the  passage  of  the  line  is  marked  by  ex- 
plosion, or  a  less  serious  method  of  yielding. 

272.  The  Causes  of  Boiler-explosions  are  numerous,  but 
are  usually  perfectly  well  understood.  Where  uncertainty  exists, 


STEAM-BOILER  EXPLOSIONS.  551 

it  is  probably  the  fact  that,  were  the  cause  ascertained,  it  would 
be  found  to  be  simple  and  well  known.  It  is  nevertheless  true 
that  some  authorities,  including  a  few  experienced  and  distin- 
guished members  of  the  engineering  profession,  believe  that 
there  are  causes,  at  once  obscure  and  of  great  potency  and  en- 
ergy, which  are  not  yet  satisfactorily  understood.  In  this  work 
the  many  causes  to  which  explosions  are,  by  various  practi- 
tioners and  writers,  attributed  may  be  divided  into  the  known, 
the  probable,  the  possible,  the  improbable,  and  the  impossible 
and  absurd. 

To  the  first  class  belong  the  general  and  fairly  uniform 
weakness  of  boilers  as  compared  with  the  steam-pressures  car- 
ried ;  the  sticking  of  safety-valves,  and  the  thousand  and  one 
other  causes  having  their  origin  in  the  ignorance,  the  carelessness, 
or  the  utter  recklessness  of  the  designer,  the  builder,  or  the  attend- 
ants intrusted  with  their  management.  To  this  class  may  be  as- 
signed the  causes  of  by  far  the  greater  proportion  of  all  explo- 
sions ;  and  the  Author  has  sometimes  questioned  whether  this 
category  may  not  cover  absolutely  all  such  catastrophes.  To 
the  second  class  may  be  assigned  "  low-water,"  a  cause  to  which 
it  was  once  customary  to  attribute  nearly  all  explosions,  but 
which  is  known  to  be  seldom  operative,  and  so  seldom  that 
some  authorities  now  question  the  possibility  of  its  action  at 
all.*  Among  the  possible  causes,  acting  rarely  and  under  pe- 
culiar conditions,  the  Author  would  place  the  overheating  of 
water,  and  the  storage  of  energy  in  excess  of  that  in  the  liquid 
at  the  temperature  due  the  existing  pressure ;  the  too  sudden 
opening  of  the  throttle-valve  or  the  safety-valve,  producing 
priming  and  shock  ;  the  spheroidal  state  of  water  ;  and  perhaps 
other  phenomena.  The  improbable  include  the  latter,  however. 
The  action  of  electricity — a  favorite  idea  with  the  uninformed 
— may  be  taken  as  an  example  of  the  impossible  and  absurd. 
The  actual  causes  of  a  vast  majority  of  boiler-explosions  are 
now  determined  by  skilled  engineers,  inspectors,  and  insurance 
experts ;  and  it  is  by  them  generally  supposed  that  no  so-called 
*  mysterious"  causes  exist,  in  the  sense  that  they  are  phenom- 

*  See  opinion  of  Mr.  J.  M.  Allen,  Sibley  College  Lecture,  Set.  Ant.  Supple- 
ment, Feb.  19,  1887,  p.  9272. 


552  THE   STEAM-BOILER. 

ena  beyond  the  present  range  of  human  knowledge  and  scien- 
tific investigation. 

All  recent  authorities  agree  in  attributing  boiler-explosions, 
almost  without  exception,  to  one  or  another  of  the  following 
general  classes  of  causes,  and  the  Author  is  inclined  to  make  no 
exception : 

(1)  Defective    design:    resulting   in   weakness  of  shell,  of 
flues,  or  of  bracing  or  staying ;  in  defective  circulation ;  faulty 
arrangement  of  parts ;    inefficiency  of  provision  for  supplying 
water  or  taking  off  steam ;  and  defects  in  arrangement  leading 
to  strains  by  unequal  expansions,  and  other  matters  over  which 
the  designer  has  control. 

(2)  Malconstruction :    including  choice  of  defective  or  im- 
proper material ;  faulty  workmanship  ;  failure  to  follow  instruc- 
tions and  drawings  ;   omission  of  stays  or  braces. 

(3)  Decay  of  the  structure  with  time  or  in  consequence  of 
lack  of  care  in  its  preservation ;   local  defects  due  to  the  same 
cause  or  to  some  unobserved  or  concealed  leakage  while  in 
operation. 

(4)  Mismanagement  in  operation,  giving  rise  to  excessive 
pressure  ;  low  water ;  or  the  sudden  throwing  of  feed-water  on 
overheated    surfaces;    or   the  production  of  other   dangerous 
conditions  ;    or  failure  to  make  sufficiently  frequent  inspection 
and  test,  and  thus  to  keep  watch  of  those  defects  which  grow 
dangerous  with  time. 

Weakness  of  boiler  or  over-pressure  of  steam  are  the  usual 
immediate  causes  of  explosions. 

It  has  often  been  suggested  that  the  most  destructive  boiler- 
explosions  may  be  attributable  to  electricity,  and  may  illustrate 
the  effect  of  an  unfamiliar  form  of  lightning.  Such  hypotheses 
are,  however,  absurd.  No  storage  and  concentration  of  elec- 
tricity could  be  produced  in  a  vessel  composed  of  the  best  of 
conducting  materials  and  enclosing  a  mass  of  fluid  incapable  of 
causing  electrical  currents,  either  great  or  small,  under  the  con- 
ditions observed  in  the  steam-boiler.  The  production  of  elec- 
tricity seen  in  Armstrong's  experiments,  a  phenomenon  some- 
times thought  to  support  this  theory,  is  simply  the  result  of 
the  friction  of  a  moving  jet  of  steam  on  the  nozzle  from  which 


STEAM-BOILER  EXPLOSIONS.  553 

it  issued,  and  presents  not  the  slightest  reason  for  supposing 
that  the  electrical  hypothesis  of  the  origin  of  boiler-explosions 
has  any  basis  of  fact. 

Professor  Faraday,  in  a  report  to  the  British  Board  of  Trade, 
May,  1859,  states  his  belief  in  the  absurdity  of  the  idea  that 
the  water  within  a  steam-boiler  may  become  decomposed,  and 
the  explosion  of  a  mixture  of  gases  so  produced  may  burst  a 
boiler: —  " .  .  .  .  As  respects  the  decomposition  of  the  steam 
by  the  heated  iron,  and  the  separation  of  hydrogen,  no  new 
danger  is  incurred.  Under  extreme  circumstances,  the  hydro- 
gen which  could  be  evolved  would  be  very  small  in  quantity, 
would  not  exert  greater  expansive  force  than  the  steam,  and 
would  not  be  able  to  burn  with  explosion,  and  probably  not  at 
all,  if  it,  with  the  steam,  escaped  through  an  aperture  into  the 
air  or  even  into  the  fire-place." 

Decomposition  cannot  occur  in  the  steam-boiler,  ordinarily; 
and  if  it  were  to  happen  in  consequence  of  low-water  and 
overheated  plates,  no  oxygen  could  remain  free  to  explosively 
combine  with  it. 

A  half-century  ago,  M.  Arago,  in  writing  of  steam-boiler 
explosions,*  asserted  that  "  no  cause  of  explosion  exists  which 
cannot  be  avoided  by  means  at  once  simple  and  within  reach 
of  every  one."  A  committee  of  the  Franklin  Institute,  in  1830, 
asserted  f  of  boiler-explosions  that  "  they  proceed,  it  is  be- 
lieved, in  most  cases,  from  defective  machinery,  improper  ar- 
rangement or  distribution  of  parts,  or,  finally,  from  carelessness 
in  management."  These  conclusions  are  fully  justified  by  all 
later  experience  ;  and  it  is  now  admitted  by  all  accepted  author- 
ities that  a  careful  examination  and  study  of  the  facts  of  the 
case  will  almost  invariably  enable  the  experienced  engineer  to 
determine  the  origin  of  the  disaster.  It  follows  that  it  is  per- 
fectly practicable  to  so  design,  construct,  and  manage  steam- 
boilers  that  there  shall  be  absolutely  no  danger  of  explosion. 

273.  The  Statistics  of  Explosions  have  been  very  care- 
fully collected  for  many  years  in  some  European  countries, 


*  Mem.  Roy.  Acad.  Sci.  Inst.  France,  xxi. 
f  Journal  Franklin  Institute,  1830. 


554 


THE   STEAM-BOILER. 


notably  in  France,  and  are  now  given  for  the  United  States  in 
very  reliable  form  by  inspectors,  governmental  and  private, 
who  are  thoroughly  familiar  with  the  subject.  The  following 
is  a  list  reported  for  the  year  1885  : 

CLASSIFIED   LIST  OF  BOILER-EXPLOSIONS. 


1 

u 

>> 

jj 

. 

u 

js 

S 

§. 

c 

rt 

J3 

M 

hi 

| 

B 

i 

3 
C 
rt 

jQ 
I 

1 

rt 
S 

'§, 

rt 

<u 

c 

3 
i—  > 

3 

CUD 
s 

< 

a 
u 

c/) 

0 

s 

§ 

V 

rt 

1 

Saw-mills  and  wood-working 

5 

2 

4 

3 

3 

o 

o 

2 

o 

<1 

T 

? 

/>O 

. 

T 

T 

T 

T 

TO 

Steamboats   tugs    etc      

2 

2 

i 

I 

I 

q 

4 

T6 

Portables,  hoisters,  and  agri- 

T 

a 

4 

2 

q 

2 

2 

T<S 

Mines,    oil  wells,     collieries, 

etc       

2 

5 

3 

2 

T 

T 

q 

T 

T 

T 

?0 

Paper-mills,  bleachers,  digest- 

T 

T 

T 

3 

Rolling-mills  and  iron-works 

I 

2 

i 

I 

I 

I 

I 

2 

10 

Distilleries,  breweries,  sugar- 

houses,    dye-houses,    ren- 

dering establishments  etc 

q 

I 

q 

I 

I 

3 

4 

2 

T  Q 

2 

i 

2 

I 

IO 

T 

T 

q 

2 

2 

I 

q 

2 

2 

T^ 

Total  per  month  

14 

20 

14 

7 

12 

12 

10 

9 

ii 

14 

15 

17 

155 

Persons   killed  —  total    220  — 

O  A 

22 

2O 

T  - 

14 

7 

j  1 

j     y 

IQ 

—    . 

1  T 

Persons  injured  —  total  288  — 

J 

. 

per  month      .      ... 

qe 

if* 

rt  Q 

Q 

q2 

6 

21 

21 

13 

4O 

22 

21 

Boilers  used  in  saw-mills  are  most  frequently  exploded,  pre- 
sumably because  of  the  cheapness  of  their  construction,  and 
the  unskilfulness  exhibited  in  their  management;  boilers  in 
mines  are  next  in  number  of  casualties.  Mill-boilers  explode 
with  comparative  infrequency.  In  the  United  States,  accord- 
ing to  the  best  estimates  which  the  Author  has  been  able  to 
make,  about  one  boiler  in  10,000  explode  among  those  which 
are  regularly  inspected  and  insured,  and  ten  times  that  proper- 


STEAM-BOILER  EXPLOSIONS. 


555 


tion  among  uninspected  and  uninsured  boilers.  In  Great 
Britain,  the  proportion  of  explosions  is  much  less  than  in  the 
United  States,  the  average  number  being  less  than  one  twentieth 
of  one  per  cent,  and  the  loss  of  life  about  three  to  every  two 
explosions.  In  Great  Britain,  as  in  the  United  States  and  else- 
where, the  majority  of  explosions  are  due  to  negligence.  Ex- 
plosions might  become  almost  unknown  were  a  proper  system 
of  inspection  and  compulsory  repair  introduced. 

The  returns  of  boiler-explosions  in  Great  Britain  and  the 
United  States  show  that  not  only  in  number  but  in  destructive- 
ness  the  record  of  the  United  States  always  exceeds  that  of 
Great  Britain,  as  is  seen  in  the  following  tables : 


No.  Explosions. 

No.  Fatalities. 

No.  Per's  Inj'd. 

1884. 

1885. 

43 

155 

1884. 

1885. 

1884. 

1885. 

Great  Britain.. 
United  States.. 

36 
152 

24 

254 

40 
22O 

49 
261 

62 
288 

No.  Explosions  per 
Million  Inhabitants. 

No.  Fatalities  per 
Explosion. 

1884. 

1885. 

1884. 

1885. 

•93 
1.42 

Great  Britain.. 
United  States.. 

I 
3 

1.17 
3-09 

.67 
1.67 

The  causes  of  the  forty-three  explosions  in  Great  Britain 
are  reported  to  have  been  : 

Cases. 

Deterioration  or  corrosion  of  boilers  and  safety-valves 20 

Defective  design  or  construction  of  boiler  or  fittings II 

Shortness  of  water 4 

Ignorance  or  neglect  of  attendants „ 4 

Miscellaneous 4 


Total, 


43 


556 


THE   STEAM-BOILER. 


For  the  United  States  there  are  estimated   to   have  been 
dangerous  cases  classified  thus : 


CAUSES. 


Whole  No. 


Dangerous. 


Deterioration  or  corrosion  of  boilers  and  safety-valves, 
Defective  design  or  construction  of  boiler  or  fittings. . . , 

Shortness  of  water , 

Ignorance  or  neglect  of  attendants , 

Miscellaneous , 


17.873 

15,895 

130 

6,404 

6,928 


1,727 

2,957 

56 

983 

1,403 


The  following  are  two  classified  lists  of  defects  and  causes 
of  dangerous  conditions,  where  in  one  case  over  6000  boilers 
and  in  the  other  above  4000  were  inspected  in  one  month  :* 


CAUSES  OF  DANGER. 


NATURE  OF  DEFECTS. 


Whole  No. 


Dangerous. 


Deposit  of  sediment 458 

Incrustation  and  scale 630 

Internal  grooving 20 

Internal  corrosion 155 

External  corrosion 346 

Broken,  loose,  and  defective  braces  and  stays 205 

Defective  settings 178 

Furnaces  out  of  shape 248 

Fractured  plates 123 

Burned  plates 89 

Blistered  plates 254 

Cases  of  defective  riveting , 1,649 

Defective  heads .......  30 

Leakage  around  tube  ends 974 

Leakage  at  seams 574 

Defective  water-gauges   163 

Defective  blow-offs 30 

Cases  of  deficiency  of  water 5 

Safety-valves  overloaded 29 

Safety-valves  defective  in  construction 42 

Defective  pressure  gauges 238 

Boilers  without  pressure-gauges 4 

Defective  hand  hole  plates 3 

Defective  hangers 13 

Defective  fusible  plugs i 

Total 6,453 


32 

55 

16 
23 
39 
17 
12 

65 

22 
II 

I87 
15 

331 
22 
27 

8 

2 

7 
7 

19 
o 

3 
o 
o 


927 


*  The  Locomotive,  December,  1884  ;  September,  1886. 


S  TEA  M-B  OILER   EXPL  0  SIONS. 


557 


NATURE  OF  DEFECTS. 


Whole  No. 


Dangerous. 


Cases  of  deposit  of  sediment 516 

Cases  of  incrustation  and  scale 78 1 

Cases  of  internal  grooving 28 

Cases  of  internal  corrosion 173 

Cases  of  external  corrosion 323 

Broken  and  loose  braces  and  stays 50 

Settings  defective 248 

Furnaces  out  of  shape 179 

Fractured  plates 108 

Burned  plates 100 

Blistered  plates 257 

Cac.es  of  defective  riveting 459 

Defective  heads 36 

Serious  leakage  around  tube  ends 461 

Serious  leakage  at  seams 205 

Defective  water-gauges 161 

Defective  blow-offs 43 

Cases  of  deficiency  of  water 18 

Safety-valves  overloaded 25 

Safety-valves  defective  in  construction 21 

Pressure-gauges  defective 215 

Boilers  without  pressure-gauges 2 

Total 4,409 


45 
54 
4 
10 
28 
13 
17 
14 
45 
25 

21 

49 
i? 
26 
27 


6 
6 
6 

26 

2 


457 


It  is  seen  that  many  of  these  defects,  all  of  which  are  danger- 
ous and  liable  to  cause  explosion,  are  of  very  variable  frequency  ; 
as,  for  example,  defective  riveting,  which  is  more  than  twice 
as  common  in  the  first  list  as  any  other  defect,  but  which 
stands  number  three  in  the  second  ;  while  other  defects  are  of 
quite  regular  occurrence,  as  the  presence  of  sediment  and  of 
scale,  grooving  and  other  corrosion,  injured  plates,  and  defective 
gauges.  Sediment,  oxidation,  and  defective  workmanship 
are  evidently  the  most  prolific  causes  of  danger;  and  unequal 
expansion,  to  which  many  of  the  reported  cases  of  leakage  are 
attributable,  hardly  less  so. 

An  inspection  of  these  tables  plainly  shows  that  the  causes 
of  steam-boiler  explosion  are  commonly  perfectly  simple,  and 
are  well  understood ;  and  a  person  familiar  with  the  subject 
usually  wonders  that  explosions  occur  as  infrequently  as  they 
do,  where  there  are  so  many  sources  of  danger,  and  where  so  little 
intelligence  and  care  is  exhibited  in  their  design,  construction, 
and  operation.  There  are,  however,  some  interesting  phenom- 


558  THE   STEAM-BOILER. 

ena  and  some  very  ingenious  theories  as  to  method  of  libera- 
tion of  the  enormous  stock  of  energy  of  which  every  boiler  is  a 
reservoir,  to  which  attention  may  well  be  given. 

274.  Theories  and  Methods  of  explosions  due  to  other 
causes  than  simple  increase  of  steam-pressure  or  decrease  in 
strength  of  boiler,  and  of  such  accidents  as  are  common  and 
well  understood,  and  produce  the  greater  number  of  disasters 
of  the  class  here  studied,  are  as  various  as  they  are  interesting. 
The  vast  majority  of  all.  boiler-explosions  have  been,  as  has  been 
seen,  found  to  be  due  to  causes  which  are  readily  detected,  and 
are  the  simplest  and  most  obvious  possible.  Here  and  there, 
however,  an  explosion  takes  place  which  is  so  exceptionally  vio- 
lent or  which  occurs  under  such  unusual  and  singular  conditions 
as  to  give  rise  to  question  whether  some  peculiar  phenomenon  is 
not  concerned  in  bringing  about  so  extraordinary  a  result.  Nearly 
all  explosions  have  been  produced  either  by  a  gradual  rise  in 
pressure  until  the  resisting  power  of  the  boiler  has  been 
exceeded  and  an  extended  rupture  liberates  the  stored  energy ; 
or  by  a  gradual  reduction  of  the  strength  of  the  structure,  until 
at  last  it  is  insufficient  to  withstand  the  ordinary  working  pres- 
sure, and  a  general  yielding  leads  to  the  same  result.  Such 
cases  require  little  comment  and  no  explanation ;  but  the  rare 
instances  in  which  a  sudden  development  of  forces  far  in  excess 
of  those  exhibited  in  regular  working  have  been  believed  to 
have  been  observed  have  given  rise  to  much  speculation,  to 
many  ingenious  theories,  and  to  an  immense  amount  of  spec- 
ulation and  misconception  on  the  part  of  those  who  are  unfa- 
miliar with  science,  and  without  experience  in  the  operation  of 
this  class  of  apparatus. 

Explosions  probably  always  occur  from  perfectly  simple  and 
easily  comprehended  causes,  are  always  the  result  of  either 
ignorance  or  carelessness,  and  are  always  preventable  where 
intelligence  and  conscientiousness  govern  the  design,  the  con- 
struction, and  the  management  of  the  boiler.  A  well-designed 
boiler,  properly  proportioned  for  its  work  and  to  carry  the 
working  pressure,  well  built,  of  good  material,  and  intelligently 
and  carefully  handled,  has  probably  never  been  known  to 
explode.  Explosions  probably  never  occur,  with  either  a  grad- 


STEAM-BOILER   EXPLOSIONS.  559 

ually  increasing  pressure  of  steam  or  decreasing  strength  of 
boiler,  unless  the  strength  of  the  structure  is  quite  uniform  ; 
local  weakness  is  a  safety-valve  which  permits  a  "  burst,"  and 
insures  against  that  more  general  disruption  which  is  called  an 
"  explosion.''  A  long  line  of  weakened  seam,  an  extended 
crack,  or  a  considerable  area  of  surface  thinned  by  corrosion 
may  lead  to  an  explosion  and  a  general  breaking  up  of  the 
whole  apparatus  ;  but  any  minor  defect,  where  its  site  is  sur- 
rounded by  strong  parts,  will  not  be  likely  to  produce  that 
result. 

The  Method  of  Explosion  is  in  the  great  majority  of 
cases  the  opening  of  a  small  orifice  at  a  point  of  minimum 
strength,  with  outrush  of  water  or  steam,  or  both  ;  the  rapid 
extension  of  the  rupture  until  it  becomes  so  great  and  the 
operation  is  so  sudden  that,  no  time  being  given  for  the  gradual 
discharge  of  the  enclosed  fluids,  the  boiler  is  torn  violently 
apart  by  the  internal  unrelieved  pressure  and  distributed  in 
pieces,  the  number  of  which  is  determined  by  the  character  and 
extent  of  the  lines  or  areas  of  weakness. 

275.  Clark  and  Colburn's  Theory  of  boiler-explosions 
has  been  accepted  as  a"  working  hypothesis"  by  many  engineers, 
and  has  some  apparent  foundation  in  experimentally  ascer- 
tained fact.  This  theory  is  attributed  to  Mr.  Zerah  Colburn  ;* 
but  was  probably,  as  stated  by  Mr.  Colburn  himself,  original 
with  Mr.  D.  K.  Clark,  who  suggests  that  a  rupture  initiated  at 
the  weakest  part  of  a  boiler,  above  or  near  the  water-line,  may 
be  extended,  and  an  explosion  precipitated  by  the  impact  of  a 
mass  of  water  carried  toward  it  by  the  sudden  outrush  of  a 
large  quantity  of  steam,  precisely  as  the  "  water-hammer"  ob- 
served so  frequently  in  steam-pipes  causes  an  occasional  rup- 
ture of  even  a  sound  and  strong  pipe.  In  fact,  many  instances 
have  been  observed  in  which  the  rent  thus  presumed  to  have 
been  produced  has  extended  not  only  along  lines  of  reduced 
section,  but  through  solid  iron  of  full  thickness  and  of  the  best 
quality.  It  is  thus  that  Mr.  Clark  would  account  for  the  shat- 


*  Steam-boiler  Explosions.      Zerah  Colburn.     London:  John  Weale.     i8fo. 


560  THE    STEAM-BOILER. 

tering  and  the  deformation  of  portions  of  the  disrupted  boiler, 
which  are  often  the  most  striking  and  remarkable  phenomena 
seen  in  such  cases. 

Colburn  suggests  that  the  explosion,  in  such  cases,  although 
seemingly  instantaneous,  may  actually  be  a  succession  of  oper- 
ations, three  or  four  at  least,  as  the  following  : 

(\\  The  initial  rupture  under  a  pressure  which  may  be  and 
probably  often  is  the  regular  working  pressure  ;  or  it  may  be  an 
accidentally  produced  higher  pressure  ;  the  break  taking  place 
in  or  so  near  the  steam-space  that  an  immediate  and  extremely 
rapid  discharge  of  steam  and  water  may  occur. 

(2)  A  consequent  reduction  of  pressure  in  the  boiler  and  so 
rapid  that  it  may  become  considerable  before  the  inertia  of  the 
mass  of  water  will  permit  its  movement. 

(3)  The  sudden  formation  of  steam  in  great  quantity  with- 
in the  water,  and  the  precipitation  of  heavy  masses  of  water, 
with  this  steam,  toward  the  opening,  impinging  upon  adjacent 
parts  of  the  boiler  and   breaking  it   open,  causing  large  open- 
ings or  extended  rents. 

(4)  The  completion  of  the  vaporization  of  the  now  liberated 
mass  of  water  to  such  extent  as  the  reduction  of  the  tempera- 
ture may  permit,  and  the  expansion  of  the  steam  so  formed, 
projecting  the  detached  parts  to  distance  depending  on  the  ex- 
tent and  rapidity  of  this  action. 

This  series  of  phenomena  may  evidently  be  the  accompani- 
ment of  any  explosion,  to  whatever  cause  the  initial  rupture 
may  be  due.  One  circumstance  lending  probability  to  this 
theory  is  the  rarity  of  explosions  originating  in  the  failure  of 
"  water-legs"  or  other  parts  situated  far  below  the  water-line. 
This  occasionally  happens,  as  was  seen  some  time  ago  at  Pitts- 
burg  in  the  explosion  of  a  vertical  boiler  caused  by  a  crack  in 
the  water-leg ;  but  it  is  almost  invariably  observed  that  explo- 
sions occur  where  long  lines  of  weakened  metal,  defective 
seams,  or  of  "  grooving"  extend  nearly  or  quite  to  the  steam- 
space.*  A  local  defect  well  below  the  water-line  would 


*  The  Westfield  explosion  illustrates  this  case.     Jour.  Frank  Inst.  1875. 


STEAM-BOILER  EXPLOSIONS.  561 

usually  simply  act  as  a  safety-valve,  discharging  the  contents 
of  the  boiler  without  explosion. 

276.  Corroboratory  Evidence  has  been  here  and  there 
found.  Lawson's  experiments,  and  those  of  others,  as  well  as 
many  accidental  explosions,  have  supplied  evidence  somewhat 
but  not  absolutely  corroboratory  of  the  Clark  and  Colburn  the- 
ory. Mr.  D.  T.  Lawson  having  become  convinced  of  the 
truth  of  the  Clark  and  Colburn  theory,  further  conceived  the 
idea  that  the  opening  and  sudden  closing  of  the  throttle  or 
the  safety-valve  might  cause  precisely  the  same  succession  of 
phenomena,  and  lead  to  the  explosion  of  boilers,  the  opening 
starting  the  current  and  the  closing  of  the  valve  producing 
impact  that  may  disrupt  the  boiler.  To  test  the  truth  of  his 
hypothesis,  he  made  a  number  of  experiments,  and  succeeded 
in  exploding  a  new  and  strong  boiler  at  a  pressure  far  below 
that  which  it  had  immediately  before  safely  borne.  As  a 
preventive,  he  proposed  the  introduction  of  a  perforated 
sheet-iron  diaphragm  dividing  the  interior  of  the  boiler  at  or 
near  the  water-line  ;  the  expectation  being  that  it  would  check 
the  action  described  by  Colburn  and  prevent  that  percussive 
effect  to  which  explosion  was  attributed  by  him,  and  also  that  it 
would  be  found  to  possess  some  other  advantages. 

The  experiments  were  made  at  Munhall,  near  Pittsburgr 
Pa.,  in  March,  1882,  the  boiler  being  of  the  cylindrical  variety^ 
30  inches  (76  cm.)  in  diameter  and  6j  feet  (2.06  m.)  in  length, 
of  iron  T3F  inch  (0.48  cm.)  in  thickness.  Its  strength  was  esti- 
mated at  430  pounds  per  square  inch  (28-$  atmos.).  Tt  was 
fitted  with  a  diaphragm,  as  above  described. 

After  some  preliminary  tests,  the  following  were  made,* 
the  valve  being  opened  at  intervals  and  suddenly  closed  again 
at  the  pressures  given  below,  as  taken  from  the  log.  A  steam- 
gauge  was  attached  to  the  boiler  above  and  one  below  the  dia- 
phragm. The  boiler  contained  18  inches  of  water.  Steam 
was  generated  slowly,  and  when  the  pressure  had  reached  50 
pounds  operating  the  discharge  valve  began  with  the  following 
results: 

*  Report  of  U.  S.  Inspectors  to  the  Secretary  of  the  Treasury,  March  23,  1882. 
36 


THE   STEAM-BOILER. 


| 

STEAM-GAUGE  ABOVE 

STEAM-GAUGE  BELOW  THE 

STEAM-PRESSURE 

AT    WHICH 

DIAPHRAGM. 

DIAPHRAGM. 

DISCHARGE-VALVE 
WAS  RAISED. 

Needle  fell 

Needle  rose 

Needle  fell 

Needle  rose 

below 

above 

below 

above 

Pounds. 

Pounds. 

Pounds. 

Pounds. 

Pounds. 

50 

7 

3 

3 

00 

80 

10 

7 

4 

00 

100 

12 

7 

5 

3 

125 

15 

15 

8 

4 

150 

2O 

20 

8 

7 

175 

15 

23 

10 

10 

200 

20 

20 

15 

oo 

225 

30 

20 

12 

oo 

230 

40 

30 

10 

00 

250 

25 

20 

10 

00 

275 

30 

25 

15 

oo 

300 

40 

35 

15 

oo 

When  the  pressure  in  the  boiler  reached  300  pounds  to  the 
square  inch  it  was  decided  that  the  boiler  had  been  sufficiently 
tested,  and  the  boiler  was  emptied  and  inspected.  The  rivets, 
seams,  and  all  the  other  parts  of  the  boiler  were  examined,  and 
no  strain,  rupture,  or  weakness  was  discovered.  The  diaphragm 
was  then  cut  out,  leaving  the  flanges  riveted  to  the  sides  of  the 
shell  and  across  the  heads.  The  boiler  was  then  again  tested 
with  the  following  results  : 


STEAM-GAUGE  ATTACHED 

STEAM-GAUGE  ATTACHED 

STEAM-  PRESSURE 

TO  THE  BOILER 

TO  BOILER  IN  WATER- 

AT    WHICH 

IN  THE  STEAM-SPACE. 

SPACE. 

DISCHARGE-VALVE 

! 

WAS    RAISED. 

Needle  fell 

Needle  rose  '   Needle  fell 

Needle  rose 

below 

above 

below 

above 

Pounds. 

Pounds. 

Pounds. 

Pounds. 

Pounds. 

100 

3 

OO 

3 

OO 

125 

2 

OO 

3 

OO 

ISO 

5 

00 

5 

00 

175 

4 

2 

3 

2 

2OO 

5 

OO 

5 

OO 

2IO 

3 

00 

3 

00 

225 

5 

OO 

3 

OO 

235 

Exploded. 

When  the  discharge-valve  was  opened  at  235  pounds  pressure 
it  caused  the  explosion  of  the  boiler.     It  was  blown  into  frag- 


•      STEAM-BOILER  EXPLOSIONS. 

ments.  The  iron  was  torn  and  twisted  into  every  conceivable 
shape ;  strips  of  various  sizes  and  proportions  were  found  in  all 
directions.  The  boiler  did  not  always  tear  at  the  seams,  but 
principally  in  the  solid  parts  of  the  iron.  At  the  time  of  the 
explosion  the  water-line  was  higher  than  during  the  test  imme- 
diately preceding.  At  an  earlier  privately  made  experiment,  as 
reported  by  the  same  investigator,  an  explosion  of  a  new  boiler 
had  been  similarly  produced  at  one  half  the  pressure  which  it 
had  been  estimated  that  the  boiler  might  sustain.  A  significant 
fact  exhibited  in  the  record  is  the  enormously  greater  fluctua- 
tion of  pressure  in  the  boiler  during  the  first  than  during  the 
second  trial,  and  the  difference  in  the  amount  of  that  fluctuation 
above  and  below  the  diaphragm. 

The  result  of  this  action  in  the  ordinary  operation  of  the 
safety-valve  or  of  the  throttle-valve  is  apparently  extremely  un- 
certain. Many  explosions  have  occurred  under  such  circum- 
stances as  would  seem  to  indicate  the  probability  of  the  action 
above  described  having  been  their  cause,  the  disaster  following 
the  opening  of  safety-valves,  or  of  the  throttle  at  starting  the 
engine. 

On  the  other  hand,  these  operations  are  of  constant  occur- 
rence, and  with  weak  and  dangerous  boilers,  yet  such  explo- 
sions are  known  to  be  extremely  rare.  The  Author,  while  offi- 
cially engaged  in  attempting  the  experimental  production  of 
boiler-explosions,  as  a  member  of  the  U.  S.  Board  appointed 
for  that  purpose,  made  numerous  experiments  of  this  nature, 
but  never  succeeded  in  producing  an  explosion.  The  danger 
would  seem  to  be,  fortunately,  less  than  it  might  be,  judged 
from  the  above.  The  introduction  of  feed-water  into  the 
steam-space  of  boilers,  producing  sudden  removal  of  pressure 
from  the  surface  of  the  water,  is  sometimes  supposed  to  have 
caused  explosions.  The  explosion  of  a  battery  of  several  boil- 
ers simultaneously— not  an  infrequent  case — is  supposed  to  be 
attributable  to  the  action  described  above,  following  the  rup- 
ture of  some  one  of  the  set. 

That  this  action  can  have  more  than  a  slight  effect,  and  that 
it  can  do  more  than  accelerate  the  rupture  of  a  weak  boiler  and 


564  THE    STEAM-BOILER. 

intensify  the  effects  of  explosions  due  to  the  action  of  other 
phenomena,  remains  to  be  proven  by  further  investigation. 

Mr.  J.  G.  Heaffman,  writing  in  1867,*  anticipated  Mr.  Law- 
son's  idea,  and,  after  describing  an  explosion  of  a  bleaching- 
boiler,  to  which  the  steam  was  supplied  from  a  separate  steam- 
boiler,  attributes  the  catastrophe  to  impact  of  water  against  the 
shell  on  the  accidental  production  of  an  opening  at  the  man- 
hole, and  asserts  that  explosions  thus  occur,  not  only  from  ex- 
cess of  pressure,  but  also  from  shock.  He  further  states  that, 
in  accordance  with  a  request  made  by  the  Association  of  Ger- 
man Engineers,  a  commission  of  the  Breslau  Association,  ex- 
perimenting with  a  small  glass  boiler,  found  that  when  the 
escape-pipes  are  only  gradually  opened,  and  the  steam  allowed 
gradually  to  escape,  the  generation  of  steam  quietly  continues 
and  the  water  remains  tranquil.  But  if  the  valve  is  quickly 
opened,  steam-bubbles  suddenly  form  all  through  the  water, 
and  rising  to  the  surface,  produce  violent  commotion.  In  one 
of  these  experiments  it  was  his  duty  to  watch  the  manometer, 
while  another  person  quickly  opened  the  valve  to  allow  the 
steam  to  escape.  As  soon  as  the  valve  was  opened  the  pres- 
sure fell  3  pounds,  but  immediately  again  began  to  rise,  and  the 
boiler  exploded.  Where  it  had  been  in  contact  with  the  water 
it  was  shattered  to  powder,  which  lay  around  like  fine  sand.  Of 
the  entire  boiler  only  a  few  small  pieces  of  the  size  of  a  dollar 
were  left.  Afterwards  they  constructed  a  similar  glass  boiler, 
with  a  cylinder  7  inches  in  diameter  and  9  inches  in  length, 
and  to  the  ends  metal  heads  were  fastened  ;  in  the  heads  were 
pipes  for  leading  in  the  steam.  By  means  of  a  force-pump  the 
boiler  was  filled  with  boiling  water,  the  valve  being  left  open 
meanwhile,  in  order  that  its  sides  might  become  evenly  heated. 
Then  half  the  water  was  drawn  off,  and  air  let  in,  and  after- 
wards more  boiling  water  forced  in,  so  that  the  air  was  com- 
pressed, until  the  boiler  exploded  at  a  pressure  of  15  atmos- 
pheres. 

The  report  was  not  nearly  as  loud  as  at  the  former  explo- 
sion, which  took  place  at  a  pressure  of  only  three  atmospheres, 

*  Journal  of  Assoc.  of  German  Engineers,  1867  ;  Iron  Age,  1867. 


STEAM-BOILER   EXPLOSIONS.  565 

and  the  glass  was  only  broken  into  several  pieces.  This,  Mr. 
Heaffman  considers,  proves  that  the  action  of  the  water  on  the 
boiler  is  such  as  would  be  produced  by  exploding  nitro-glycer- 
ine  in  the  water.  He  goes  on  to  state  that  in  bleacheries,  dye- 
works,  etc.,  the  habit  often  prevails  of  suddenly  opening  the 
steam-cocks,  thus  endangering  the  boiler. 

He  does  not  assert  that  every  time  a  cock  is  suddenly 
opened  an  explosion  must  follow  ;  but  that  it  may  take  £>lace, 
experience  has  shown.  In  the  experiments  above  described 
they  had  many  times  opened  the  glass  boiler  without  causing 
an  explosion  ;  with  the  second  boiler,  too,  they  had  done  so 
without  being  able  to  bring  about  explosion,  both  with  high 
and  low  pressure.  In  the  former  class  of  explosions  the 
steam  shatters,  twists,  and  contorts  everything  in  an  instant. 

"  Water-hammer'  has,  by  the  bursting  of  steam-pipes,  by  a 
process  somewhat  closely  related  to  that  described  by  Clark 
and  Colburn,  sometimes  caused  fatal  injury  to  those  near  at 
the  instant  of  the  accident.  This  is  a  phenomenon  which  has 
long  been  familiar  to  engineers,  and  the  author  has  been  cog- 
nizant of  many  illustrations,  in  his  own  experience,  of  its 
remarkable  effects,  and  has  sometimes  known  of  almost  as  seri- 
ous losses  of  life  as  from  boiler-explosions.  It  is  rarely  the 
cause  of  serious  loss  of  property. 

When  a  pipe  contains  steam  under  pressure,  and  has  intro- 
duced into  it  a  body  of  cold  water,  or  when  a  cold  pipe  con- 
taining water  is  suddenly  filled  with  steam,  the  contact  of  the 
two  fluids,  even  when  the  water  is  in  very  small  quantities, 
results  in  a  sudden  condensation  which  is  accompanied  by  the 
impact  of  the  liquid  upon  the  pipe  with  such  violence  as  often 
to  cause  observable  or  even  very  heavy  shocks ;  and  often  a 
succession  of  such  blows  is  heard,  the  intensity  of  which  is  the 
greater  as  the  pipe  is  heavier  and  larger,  and  which  may  be 
startling,  and  even  very  dangerous.  It  is  not  known  precisely 
how  this  action  takes  place ;  but  the  Author  has  suggested 
the  following  as  a  possible  outline  of  this  succession  of  phe 
nomena:* 

*  "  Water-hammer  in  Steam-pipes."    Trans.  Am.  Soc.  Mech.  Engrs.,  vol.  iv. 
p.  404. 


$66  THE   STEAM-BOILER. 

The  steam,  at  entrance,  passes  over  or  comes  in  contact 
with  the  surface  of  the  cold  water  standing  in  the  pipe.  Con- 
densation occurs,  at  first  very  slowly,  but  presently  more 
quickly,  and  then  so  rapidly  that  the  surface  is  broken,  and 
condensation  is  completed  with  such  suddenness  that  a  vacuum 
is  produced.  The  water  adjacent  to  this  vacuum  is  next  pro- 
jected violently  into  the  vacuous  space,  and,  filling  it,  strikes 
on  the  metal  surfaces  and  with  a  blow  like  that  of  a  solid  body, 
the  liquid  being  as  incompressible  as  a  solid.  The  intensity  of 
the  resulting  pressure  is  the  greater  as  the  distance  through 
which  the  surface  attacked  can  yield  is  the  less,  and  enormous 
pressures  are  thus  attained,  causing  the  leakage  of  joints,  and 
even  the  straining,  twisting,  and  bursting  of  pipes.  In  some 
cases  the  whole  of  an  extensive  line  or  system  of  pipes  has 
been  observed  to  writhe  and  jump  to  such  extent  as  to  cause 
well-grounded  apprehension. 

The  Author  once  had  occasion  to  test  the  strength  of  pipes 
which  had  been  thus  already  burst.  They  were  8  inches  in 
diameter  (20.32  cm.),  and  of  a  thickness  of  f  inch  (0.95  cm.),  and 
had  been,  when  new,  subjected  to  a  pressure  of  about  20  at- 
mospheres (300  Ibs.  per  sq.  in.).  When  tested  by  the  Author 
in  their  injured  condition  they  bore  from  one  third  more  to 
nearly  four  times  as  high  pressures  before  the  cracks  which  had 
been  produced  were  extended.  It  is  perhaps  not  absolutely 
certain  that  some  of  these  pieces  of  pipe  may  not  have  been 
cracked  at  lower  pressures  than  the  above ;  but  it  is  hardly 
probable.  It  seems  to  the  Author  very  certain  that  the  pres- 
sures attained  in  his  tests  were  approximately  those  due  to 
the  water-hammer,  or  were  lower.  The  steam-pressure  had 
never  exceeded  about  four  atmospheres  (60  Ibs.  per  sq.  in.). 

It  is  evident  that  it  is  not  safe,  in  such  cases,  to  calculate 
simply  on  a  safe  strength  based  on  the  proposed  steam-pres- 
sures; but  the  engineer  may  find  those  actually  met  with 
enormously  in  excess  of  boiler-pressure,  and  a  "  factor-of-safety>v 
of  20  may  prove  too  small,  it  being  found,  as  above,  that  the 
water-hammer  may  produce  local  pressure  approaching,  if  not 
exceeding,  70  atmospheres  (1000  Ibs.  per  sq.  in.).  These  facts, 


STEAM-BOILER  EXPLOSIONS.  $6? 

now  well  ascertained  and  admitted,  lend  some  confirmation  to 
the  Clark  and  Colburn  theory  of  explosions. 

277.  Energy  Stored  in  Heated  Metal  is  vastly  less  in 
amount,  with  the  same  range  of  temperature,  than  in  water. 
The  specific  heat  of  iron  is  but  about  one  ninth  that  of  water, 
and  the  weight  of  metal  liable  to  become  overheated  in  any 
boiler  is  usually  small.  If  the  whole  crown-sheet  of  a  locomo- 
tive-boiler were  to  be  heated  to  a  full  red  heat,  it  would  only 
store  about  as  much  heat  per  degree  as  forty  pounds  (18  kgs.) 
of  water,  or  not  far  from  30,000  thermal  units  (7560  calories),  or 
23,016,000  foot-pounds  (3,030,000  kilog.-m.,  nearly),  or  about 
three  tenths  of  the  total  energy  of  the  fluids  concerned  in  the 
explosion.  It  would  be  sufficient,  however,  to  considerably  in- 
crease the  quantity  of  steam  present  in  the  steam-space  ;  and 
this  increase,  if  suddenly  produced,  and  too  quickly  for  the 
prompt  action  of  the  safety-valve,  might  evidently  precipitate 
an  explosion,  which  would  be  measured  in  its  effects  by  the 
total  energy  present. 

It  thus  becomes  at  once  obvious  that  the  danger  from  the 
presence  of  this  stock  of  excess  energy  is  determined  not  only 
by  the  weight  of  metal  heated  and  its  temperature,  but  even 
more  by  the  rate  at  which  that  surplus  heat  is  communicated 
to  the  water  that  may  be  brought  in  contact  with  it,  by  pump- 
ing in  feed-water,  or  by  any  cause  producing  violent  ebullition. 
It  is  probable  that  this  cause  has  sometimes  operated  to  pro- 
duce explosions  ;  but  oftener  that  the  loss  of  strength  pro- 
duced by  overheating  is  the  more  serious  source  of  danger.  It 
is  also  evident  that  the  first  is  the  more  dangerous  as  the  pres- 
sures are  lower,  the  second  with  high  pressures. 

As  illustrating  a  calculation  in  detail,  assume 


range  of  temperature,  into  specific  heat  (o.m),  is  the  measure 
of  the  heat-energy  stored. 


of    crown-sheet,    or   boiler-shell,    overheated  •!  T/;;Lo  T-'  f  >  tne 

i  i  ooo    Jr  •  \ 

metal   being   {  £  ^centimetres  J    in    thicknesSj    and    its    total 
weight       I7°kll°V      .      Then   the    product    of   weight    into 


568  THE   STEAM-BOILER. 

375  X  1000  X  o.i  1 1  —41,625  B.  T.  U.,  nearly; 
17°  X     556  X  o.i  1 1  =10,492  calories,  nearly; 

and  in  mechanical  units, 

41,625  X  772       =  32,134,500  foot-pounds  nearly; 
10,502  X  423.55  =    4,443,886  kilog.-metres  nearly; 

which  is  fifteen  or  twenty  times  the  energy  stored  in  the  steam 
in  a  locomotive-boiler  in  its  normal  condition,  and  about  one 
half  as  much  as  ordinarily  exists  in  water  and  steam  together. 
It  is  evident  that  the  limit  to  the  destructiveness  of  explosions 
so  caused  is  the  rate  of  transfer  of  this  energy  to  the  water 
thrown  over  the  hot  plate,  and  the  promptness  with  which  the 
steam  made  can  be  liberated  at  the  safety-valve.  A  sudden 
dash  of  water  or  spray  over  the  whole  of  such  a  surface  might 
be  expected  to  even  produce  a  "fulminating"  explosion.  For- 
tunately, as  experience  has  shown,  so  sudden  a  transfer  or  so 
complete  a  development  of  energy  rarely,  perhaps  never,  takes 
place. 

278.  The  Strength  of  Heated  Metal  is  known  usually  to 
decrease  gradually  with  rise  in  temperature,  until,  as  the  weld- 
ing or  the  melting-point,  as  the  case  may  be,  is  approached,  it 
becomes   incapable  of  sustaining  loads.     Both  iron  and  steel, 
however,  lose  much  of  their  tenacity  at  a  bright-red  heat,  at 
which  point  they  have  less  than  one  fourth  that  at  ordinary 
temperatures.     A  steam-boiler  in  which  any  part  of  the  furnace 
is  left   unprotected  by  the   falling  of  the  water-level   is   very 
likely  to  yield   to  the  pressure,  and   an   explosion   may  result 
from  simple  weakness.      At  temperatures  well  below  the  red 
heat  this  will  not  happen. 

279.  "  Low  Water,"  in  consequence  of  the  obvious  dangers 
which  attend  it,  and  the  not  infrequent  narrow  escapes  which 
have  been   known,  has   often    been   by  experienced  engineers 
considered  to  be  the  most  common,  even  the  almost  invariable, 
cause  of  explosions.     This  view  is  now  refuted   by  statistics 
and  a  more  extended  observation  and  experience  ;  but   it   re- 
mains one  of  the  undeniable  sources  of  danger  and  causes  of 
accident. 

Its  origin  is  usually  in  some  accidental  interruption  of  the 


STEAM-BOILER  EXPLOSIONS.  569 

supply  of  feed-water ;  less  often  an  unobserved  leak  or  ac- 
celerated production  of  steam.  Whatever  the  cause,  the 
result  is  the  uncovering  of  those  portions  of  the  heating- 
surface  which  are  highest,  and  their  exposure,  unprotected 
by  any  efficient  cooling  agency,  to  the  heat  of  the  gases 
passing  through  the  flue  at  that  point.  Should  it  be  the 
case  of  a  locomotive  or  other  boiler  having  the  crown-sheet  of 
its  furnace  so  placed  as  to  be  first  exposed  when  the  water- 
level  falls,  the  iron  may  become  heated  to  a  full  red  heat ;  if 
the  highest  surfaces  are  those  of  tubes,  through  which  gases 
approximating  the  chimney  in  temperature  are  passing,  the 
heat  and  the  danger  are  less.  In  either  case  danger  is  incurred 
only  when  the  temperature  becomes  such  as  to  soften  the  iron, 
or  when  the  return  of  the  water  with  considerable  rapidity 
gives  rise  to  the  production  of  steam  too  rapidly  to  be  relieved 
by  the  safety-valve  or  other  outlet.  Such  explosions  probably 
very  seldom  actually  occur,  even  when  all  conditions  seem  fa- 
vorable. Every  boiler-making  establishment  is  continually  col- 
lecting illustrations  of  the  fact  that  a  sheet  may  be  overheated, 
and  may  even  alter  its  form  seriously  when  overheated,  without 
completely  yielding  to  pressure;  and  the  Author  has  taken 
part  in  many  attempts  to  experimentally  produce  explosions 
by  pumping  feed-water  into  red-hot  boilers,  and  has  but  once 
seen  a  successful  experiment.  The  same  operation,  in  the  reg- 
ular workings  of  boilers,  has  been  often  performed  by  ignorant 
or  reckless  attendants  without  other  disaster  than  injury  to  the 
boiler,  but  it  has  unquestionably  on  other  occasions  caused 
terrible  loss  of  life  and  property.  The  raising  of  a  safety-valve 
on  a  boiler  in  which  the  water  is  low,  by  producing  a  greater 
violence  of  ebullition  in  the  water  on  all  sides  the  overheated 
part,  may  throw  a  flood  of  solid  water  or  of  spray  over  it ;  and 
it  is  probable  that  this  has  been  a  cause  of  many  explosions. 
The  Author  has  seen  but  a  single  explosion  produced  in  this 
way,  although  he  has  often  attempted  to  so  produce  such  a  re- 
sult. In  three  experiments  on  a  plain  cylindrical  boiler,  empty 
and  heated  to  the  red  heat,  the  result  of  rapidly  pumping  in  a 
large  quantity  of  water  was  in  the  first  the  production  of  a 
vacuum,  in  the  second  an  excess  of  pressure  safely  and  easily 


57°  THE   STEAM-BOILER. 

relieved  by  the  safety-valve,  and  in  the  third  case  a  violent  ex- 
plosion of  the  boiler  and  the  complete  destruction  of  the  brick 
masonry  of  its  setting.*  A  committee  of  the  Franklin  Institute, 
conducting  similar  experiments, f  had  the  same  experience, 
the  pressure  "  rising  from  one  to  twelve  atmospheres  within 
two  minutes"  after  starting  the  pump.  The  most  rapid  vapor- 
ization occurs,  as  is  well  known,  at  a  comparatively  low  temper- 
ature of  metal ;  at  high  temperature  the  spheroidal  condition  is 
produced,  and  no  contact  exists  between  metal  and  liquid. 

Mr.  C.  A.  Davis,  President  of  the  New  York  and  Boston 
Steamboat  Co.,  in  a  letter  addressed,  Dec.  7,  1831,  to  the  Col- 
lector of  the  Port  of  New  York,  and  answering  inquiries  of  the 
United  States  Treasury  Department,  wrote  \\ 

"  I  have  noted  that  by  far  the  greatest  number  of  accidents 
by  explosion  and  collapsing  of  boilers  and  flues — I  might  say 
seven  tenths — have  occurred  either  while  the  boat  was  at  rest,  or 
immediately  on  starting,  particularly  after  temporary  stoppages 
to  take  in  or  land  passengers.  These  accidents  may  occur  from 
directly  opposite  causes — either  by  not  letting  off  enough  steam, 
or  by  letting  off  too  much:  the  latter  is  by  far  the  most  de- 
structive." 

The  idea  of  this  writer  was  that  the  "  letting  off  of  too  much  " 
steam,  producing  low-water,  was  the  most  frequent  cause  of 
explosions — an  idea  which  has  never  since  been  lost  sight  of. 

The  chief-engineer  of  the  Manchester  (G.  B.)  Steam-boiler 
Association,  in  1866-67,  repeatedly  injected  water  into  over- 
heated steam-boilers,  but  never  succeeded  in  producing  an 
explosion.§  Yet,  as  has  been  seen,  such  explosions  may  occur. 

A  writer  in  the  Journal  of  the  Franklin  Institute,!  a  half- 
century  or  more  ago,  asserted  that  "  the  most  dreadful  accidents 
from  explosions  which  have  taken  place  have  occurred  from 
low-pressure  boilers."  It  was,  as  he  states,  "a  fact  that  more 
persons  had  been  killed  by  low  than  by  high  pressure  boilers." 


*  Set.  Am.,  Sept.  1875. 
f  Jour.  Franklin  Inst.  1837,  vol.  xvii. 
|  Report  on  Steam-boilers,  H.  R.,  1832. 
§  Mechanics'  Magazine,  May,  1867. 
||  Vol.  iii.  pp.  335,  418,  420. 


STEAM-BOILER  EXPLOSIONS.  571 

Nearly  all  writers  of  that  time  attributed  violent  explosions  to 
low-water,  and  some  likened  the  phenomenon  to  that  observed 
when  the  blacksmith  strikes  with  a  moist  hammer  on  hot  iron. 

Thus,  if  the  boiler  is  strong,  and  built  of  good  iron,  and  not 
too  much  overheated,  or  if  the  feed-water  is  introduced  slowly 
enough,  it  is  possible  that  it  may  not  be  exploded ;  but  with 
weaker  iron,  a  higher  temperature,  or  a  more  rapid  development 
of  steam,  explosion  may  occur.  Or,  if  the  metal  be  seriously 
weakened  by  the  heat,  the  boiler  may  give  way  at  the  ordinary 
or  a  lower  pressure ;  which  result  may  also  be  precipitated  by  the 
strains  due  to  irregular  changes  of  dimensions  accompanying 
rapid  and  great  changes  of  temperature. 

Explosions  due  to  low-water,  when  there  is  a  considerable 
mass  of  water  below  the  level  of  the  overheated  metal,  are  some- 
times fearfully  violent ;  a  boiler  completely  emptied  of  water? 
and  only  exploded  by  the  volume  of  steam  contained  within  it, 
is  far  less  dangerous.  Low-water  and  red-hot  metal  in  a  loco- 
motive or  other  firebox  boiler  are  for  this  reason  far  more  dan- 
gerous than  in  a  plain  cylindrical  boiler,  since,  as  was  indicated 
by  the  experiments  conducted  by  the  Author,  the  latter  must  be 
entirely  deprived  of  water  before  this  dangerous  condition  can 
arise.  In  the  course  of  the  numerous  experiments  already  al- 
luded to,  many  attempts  were  made  to  overheat  the  latter  class 
of  boiler;  but  none  were  successful  until  the  water  was  entirely 
expelled.  Experiments  with  apparatus  devised  for  the  purpose 
of  keeping  the  steam  moist  under  all  circumstances  indicate 
that  it  is  difficult  if  not  impossible  to  overheat  even  an  un- 
covered firebox  crown-sheet  if  the  steam  be  kept  moist,  and 
that  such  steam  is  very  nearly  as  good  a  cooling  medium,  in 
such  cases,  as  the  water  itself. 

Fig.  125*  represents  a  boiler  exploded  by  the  introduction 
of  water  after  it  had  been  emptied  by  carelessly  leaving  open 
the  blow-cock.  This  boiler  was  about  five  years  old  ;  and  the 
explosion,  as  is  usual  in  such  cases,  was  not  violent,  the  small 
amount  of  water  entering  and  the  weakness  of  the  sheet  con- 
spiring to  prevent  the  production  of  very  high  pressure  or  the 

*  The  Locomotive,  Sept.  1886,  p.  129. 


572  THE   STEAM-BOILER. 

storage  of  much  energy.  The  whole  of  the  lower  part  of  the 
shell  of  the  boiler  was  found,  on  subsequent  examination,  to 
have  been  greatly  overheated.  One  man  was  killed  by  the  fall- 
ing of  the  setting  upon  him ;  no  other  damage  was  done. 


FIG.  125.— BOILER  EXPLODED.     CAUSE,  LOW-WATER. 

Fig.  126  shows  the  effect  of  a  similar  operation  on  a  water- 
tube  boiler.  The  feed-water  was  cut  off,  and  not  noticed  until 

the  water-level  became  so  low  that 
the  boiler  was  nearly  empty  and 
the  tubes  were  overheated.  One 

FIG.  I26.-TUBE  BURST:  LOW-WATER.       Qf  the  tubes  burstj  and  the  Damage 

was  speedily  repaired   at  a  cost  of  $15,  and   the  works  were 
running  the  next  day.* 

That  low-water  and  the  consequent  overheating  of  the 
boiler  does  not  necessarily  produce  disaster,  ev«n  when  the 
water  is  again  supplied  before  cooling  off,  was  shown  as  early 
as  1811,  by  the  experience  of  Captain  E.  S.  Bunker  of  the 
Messrs.  Stevens'  steamboat  Hope,  then  plying  between  New 
York  and  Albany.  During  one  of  the  regular  passages  he  dis- 
covered that  the  water  had  been  allowed  by  an  intoxicated  fire- 
man to  completely  leave  both  the  boilers.  He  at  once  started 
the  pump,  and,  filling  up  the  boilers,  proceeded  on  his  way,  no 
other  sign  of  danger  presenting  itself  than  "  a  crackling  in  the 


*  G.  H.  Babcock. 


STEAM-BOILER  EXPLOSIONS.  573 

boiler  as  the  water  met  the  hot  iron,  the  sound  of  which  was 
like  that  often  heard  in  a  blacksmith's  shop  when  water  is 
thrown  on  a  piece  of  hot  iron."  ' '  A  year  later  Captain  Bunker 
repeated  this  experience  at  Philadelphia  on  the  Phoenix, 
where  the  boilers  were  of  the  same  number  and  size  as  those 
of  the  Hope.f 

Defective  circulation  may  cause  the  formation  of  a  volume 
of  steam  in  contact  with  a  submerged  portion  of  the  heating- 
surface.  The  Author,  when  in  charge  of  naval  boilers  during 
the  civil  war,  1861-5,  found  it  possible  on  frequent  occasions 
to  draw  a  considerable  volume  of  practically  dry  steam  from  the 
water-space  between  the  upper  parts  of  two  adjacent  furnaces 
at  a  point  two  or  three  feet  below  the  surface-water  level. 
After  drawing  off  steam  for  a  few  seconds,  through  a 
cock  provided  to  supply  hot  water  for  the  engine  and  fire- 
rooms,  water  would  follow  as  in  the  normal  condition  of  the 
boiler.  This  condition  often  occurs  in  some  forms  of  boiler, 
and  has  been  occasionally  observed  by  every  experienced  en- 
gineer. It  would  not  seem  impossible,  therefore,  that  steam 
might  be  sometimes  thus  encaged  in  contact  with  the  furnace, 
and  thus  cause  overheating  of  the  adjacent  metal.  Many  such 
instances  have  been  related  ;  but  they  have  been  commonly 
regarded  by  the  inexperienced  as  somewhat  apocryphal.;): 

In  order  that  the  danger  of  overheating  the  crown-sheet  of 
the  locomotive  type  of  boiler  may  be  lessened,  it  is  very  usual 
to  set  it  lower  at  the  firebox  end,  when  employed  as  a  station- 
ary boiler,  so  as  to  give  a  greater  depth  of  water  over  the 
crown-sheet  than  over  the  tubes  at  the  rear.  The  plan  of  giv- 
ing.greatest  depth  of  water,  when  possible,  at  that  end  of  the 
boiler  at  which  the  heating-surfaces  near  the  water-surface  are 
hottest  is  always  a  good  one. 

Mr.  Fletcher  concluded  from  his  experiments  that  low-water 
is  only  a  cause  of  danger  by  weaking  the  overheated  plates.  He 
says:§ 

*Doc.  No.  21,  H.  R.,  25th  Congress,  3d  Session,  1838,  p.  103. 

f  Ibid. 

\  See  London  Engineer,  Dec.   7,  1860,  pp.  371,  403. 

§  London  Engineer,  Mar.  15,  1867,  p.  228. 


574  THE   STEAM-BOILER. 

"  These  experiments,  it  is  thought,  may  be  accepted  as 
conclusive  that  the  idea  of  an  explosion  arising  from  the  in- 
stantaneous generation  of  a  large  amount  of  steam  through  the 
injection  of  water  on  hot  plates  is  a  fallacy." 

The  conclusion  of  the  Author,  in  view  of  the  experiments  of 
the  committee  of  the  Franklin  Institute  and  of  his  own  per- 
sonal experience  in  the  actual  production  of  explosions  by 
this  very  process,  as  elsewhere  described,  does  not  accord  with 
the  above  ;  but  it  is  sufficiently  well  established  that  low-water 
may  frequently  occur  and  feed-water  may  be  thrown  upon  the 
overheated  plates  without  necessarily  causing  explosion.  Dan- 
ger does,  however,  unquestionably  arise,  and  such  explosions 
have  most  certainly  occurred — possibly  many  in  the  aggre- 
gate. 

Low-water  is  certainly  very  rarely,  perhaps  almost  never, 
the  cause  of  explosion  of  other  than  firebox  boilers  ;  in  these, 
however,  the  danger  of  overheating  the  crown-sheet  of  the 
furnace,  if  the  supply  of  water  fails,  is  very  great,  and  in  such 
cases  explosion  is  always  to  be  feared.  The  most  disastrous 
explosions  are  usually  those,  however,  in  which  the  supply  of 
water  is  most  ample. 

280.  Sediment  and  Incrustation  sometimes  produce  the 
effect  of  low-water  in  boilers,  even  where  the  surfaces  affected 
are  far  below  the  surface  of  the  water.  Every  increase  of  re- 
sistance to  the  passage  of  heat  through  the  metal  and  the  in- 
crusting  layer  of  sediment  or  scale  causes  an  increase  of  tem- 
perature in  the  metal  adjacent  to  the  flame  or  hot  gases,  until, 
finally,  the  incrustation  attaining  a  certain  thickness,  the  iron 
or  steel  of  the  boiler  becomes  very  nearly  as  hot  as  the  gases 
heating  it.  Should  this  action  continue  until  a  red  heat,  or  a 
white  heat  even,  as  sometimes  actually  occurs,  is  reached,  the 
resistance  becomes  so  greatly  reduced  that  the  sheet  yields, 
and  either  assumes  the  form  of  a  "pocket"  or  depression,  as 
often  happens  with  good  iron  or  with  steel,  or  it  cracks,  or  it 
even  opens  sufficiently  to  cause  an  explosion.  "  Pockets" 
often  form  gradually,  increasing  in  extent  and  depth  day  by 
day,  until  they  are  discovered,  cut  out,  and  a  patch  or  a  new 
sheet  put  in,  or  until  rupture  takes  place.  In  such  cases  the 


STEAM-BOILER  EXPLOSIONS.  575 

incrustation    keeps   the   place    covered    while  permitting   just 
water  enough  to  pass  in  to  cause  the  extension  of  the  defect. 

In  some  cases  the  process  is  a  different  and  a  more  disas- 
trous one :  The  scale  covers  an  extended  area,  permitting  it 
to  attain  a  high  temperature.  After  a  time  a  crack  is  pro- 
duced in  the  scale  by  the  unequal  expansion  of  the  two  sub- 
stances and  the  inextensibility  of  the  incrustation ;  and  water 
entering  through  this  crack  is  exploded  into  steam,  ripping  off 
a  wide  area  of  incrustation  previously  covering  the  overheated 
sheet,  and  giving  rise  instantly,  probably,  to  an  explosion 
which  drives  the  sheet  down  into  the  fire,  and  may  also  rend 
the  boiler  into  pieces,  destroying  life  and  property  on  every 
side.  Such  an  explosion  usually  takes  place  with  the  boiler 
full  of  water  and  its  stored  energy  a  maximum,  and  the  result 
is  correspondingly  disastrous. 

Certain  greasy  incrustations  and  some  floury  forms  of  min- 
eral or  vegetable  deposits  have  been  found  peculiarly  danger- 
ous, as,  in  even  exceedingly  thin  layers,  they  are  such  perfect 
non-conductors  as  to  speedily  cause  overheating,  strains,  cracks, 
leakage,  and  often  explosion.  M.  Arago  mentions  a  case  in 
which  rupture  occurred  in  consequence  of  the  presence  of  a  rag 
lying  on  the  bottom  of  a  boiler.* 

The  effect  of  incrustation  in  causing  the  overheating  of  the 
fire-surfaces,  the  formation  of  a  "  pocket  "  and  final  rupture,  is 
well  shown  in  the  illustrations  which  follow. 

When  the  water  is  fully  up  to  the  safe  level,  as  at  the  right 
in  the  first  of  the  two  figures,  the  heat  received  from  the  fur- 
nace-gases is  promptly  carried 
away  by  the  water,  and  the  sheet 
is  kept  cool.  When  the  water 
falls  below  that  level,  or  is  pre- 
vented by  incrustation  from 
touching  the  metal,  as  in  the  left- 
hand  illustration,  the  sheet  be- 
comes red-hot,  soft,  and  weak, 
and  yields  as  shown.  When  this  goes  on  to  a  sufficient  extent, 

*  Report  of  the  Committee  of  the  Franklin  Institute. 


FIG.  127. — OVERHEATING  THE  SHEET 


5/6 


THE   STEAM-BOILER. 


as  on  a  horizontal  surface  (Fig.  128),  a  pocket  is  produced.  The 
illustration  represents  a  sheet  removed  from  the  shell  of  an  ex- 
ternally fired  boiler  thus  injured. 


FIG.  128.— A  "  POCKET.' 


Finally,  when  the  defect  is  not  observed  and  the  injured 
sheet  removed,  the  metal  may  finally  give  way  entirely,  per- 


FIG.  129. — RUPTURED  POCKET. 


mitting  the  steam  and  water  to  issue,  as  in  the  last  illustration 
of  the  series,  in  which  this  last  step  in  the  process  is  well 
represented.  Where  the  area  thus  affected  is  considerable, 


FIG.  130. — SHELL  RUPTURED. 

the  result  may  be  a  general  breaking  up  of  that  portion  of  the 
shell,  as  in  the  next  figure,  and  an  explosion  may  prove  to  be 
the  final  step  in  the  chain  of  phenomena  described.  In  other 
cases,  where,  as  in  the  next  sketch,  a  line  of  weakness  may  be 


STEAM-BOILER  EXPLOSIONS.  577 

the  result   of  other  causes,  a  large    section  of   the  boiler  may 
be  broken  out,  as  at  AD,  Fig.  131. 


FIG.  131.— EXTENDED  RUPTURE. 

The  deposition  of  sediment  and  of  scale  takes  place  not 
only  in  the  boiler,  but  also  with  some  kinds  of  water,  in 
the  feed-pipe,  as  is  illustrated  in  the 
accompanying  engraving,  which  is 
made  from  an  actual  case  in  which 
the  pipe  was  so  nearly  filled  as  to 
become  quite  incapable  of  perform- 
ing its  office.  A  current  has  appar- 
ently no  effect,  in  many  such  cases, 

in  preventing  the  deposition  of  scale.  ' IG<  1*'F££5£A™H 
The  Author  has  known  hard  scale  to  form  in  the  cones  of  a 
Giffard  injector  under  his  charge,  where  the  stream  was  mov- 
ing with  enormous  velocity,  and  loudly  whistling  as  it  passed. 

Instances  are  well  known  of  the  explosion,  with  fatal  effect, 
of  open  vessels,  in  consequence  of  the  action  above  described. 
Mr.  G.  Gurney  in  1831  gave  an  account  of  such  an  explosion 
of  the  water  in  an  open  caldron,  at  Meux's  brewery,  by  which 
one  person  was  killed  and  several  others  injured.*  It  was  found 
that  the  bottom  had  become  incrusted  with  sediment,  and  the 
sudden  rupture  of  the  film,  permitting  contact  of  the  water 
above  with  the  overheated  metal  below,  caused  such  a  sudden 
and  violent  production  of  steam  that  it  actually  ruptured  the 
vessel.  The  process  of  which  this  is  an  illustration  is  precisely 
analogous  to  suddenly  throwing  feed-water  into  an  overheated 
boiler. 

*  Report  on  Steam  Carriages.     Doc.  101,  22d  Congress,  ist  Session,  p.  31. 
37 


5/8  THE   STEAM-BOILER. 

281.  Energy  stored  in  Superheated  Water  has  been 
sometimes  considered  a  source  of  danger  to  steam-boilers  and 
a  probable  cause  of  explosions.  The  magnitude  of  this  stock 
of  energy  is  not  likely  to  differ  greatly  from  that  of  water  at 
the  same  temperature  under  the  pressure  due  that  tempera- 
ture, and  for  present  purposes  specific  heat  may  be  taken  as 
unity.  The  quantity  of  heat  so  stored  is  therefore  measured 
very  nearly  by  the  product  of  the  weight  of  water  so  overheated, 
the  mean  range  of  superheating,  and  the  specific  heat  here 
taken  as  unity.  It  is  not  known  how  large  a  part  of  the  water 
in  any  boiler  can  be  superheated,  or  the  extent  to  which  this 
action  can  occur.  It  is  often  doubted,  however,  whether  it  can 
take  place  at  all  in  steam-boilers. 

This  condition  occurring,  the  experiments  of  MM.  Donny, 
Dufour,  and  others  show  that  the  larger  the  mass  of  water 
the  less  the  degree  of  superheating  attainable  ;  the  more  im- 
pure the  water,  or  the  greater  the  departure  from  the  condi- 
tion of  distilled  water,  and  the  larger  the  proportion  of  air  or 
sediment  mechanically  suspended,  the  more  difficult  is  it  to  at- 
tain any  considerable  superheating. 

As  early  as  1812,*  Gay-Lussac  observed  a  retardation  of 
ebullition  in  glass  vessels;  thirty  years  later,f  M.  Marcet  found 
that  water  deprived  of  air  can  be  raised  seveial  degrees  above 
its  normal  boiling-point;  while  Donny, \  Dufour,§  Magnus,) 
and  Grove^f  all  succeeded  in  developing  this  phenomenon  more 
or  less  remarkably.  Donny,  sealing  up  water  deprived  of  air 
in  glass  tubes,  succeeded  in  raising  the  boiling  point  to  138°  C. 
(280°  F.),  at  which  temperature  vaporization  finally  occurred 
explosively.  Dufour,  by  floating  globules  of  pure  water  in  a 
mixture  of  oils  of  density  equal  to  that  of  the  water,  succeeded 
with  very  minute  globules  in  raising  the  boiling-point  to  175° 
C.  (347°  F.),  at  which  temperature  the  normal  tension  of  its 

*  Ann.  de  Chimie  et  de  Physique,  Ixxxii. 
|  Bibl.  Univ.  xxxviii. 

\  Ann.  de  Ch.  et  de  Phys.,  3me  serie,  xvi. 
§  Bibl.  Univ.,  Nov,  1861,  i.  xii. 
!j  Poggendorff's  Ann.  t.  cxiv. 
*[[  Cosmos,  '863. 


STEAM-BOILER  EXPLOSIONS.  579 

steam  is  115  pounds  per  square  inch  (nearly  eight  atmospheres) 
by  gauge.  In  such  cases  the  touch  of  any  solid  or  of  bubbles 
of  gas  would  produce  explosive  evaporation.  Solutions  always 
boil  at  temperatures  somewhat  exceeding  the  boiling-point  of 
water,  but  usually  quietly  and  steadily.  In  all  these  cases  the 
rise  in  temperature  seems  to  have  been  the  greater  the  smaller 
the  mass  of  water  experimented  with. 

In  all  ordinary  cases  of  steam-boiler  operation  the  mass  of 
water  is  simply  enormous  as  compared  with  the  quantities  em- 
ployed in  the  above-described  laboratory  experiments ;  the 
water  is  almost  never  pure,  and  probably  as  invariably  contains 
more  or  less  air.  It  would  seem  very  unlikely  that  such  super- 
heating could  ever  occur  in  practice.  There  is,  however,  some 
evidence  indicating  that  it  may. 

Mr.  Wm.  Radley*  reports  experimenting  with  small  labora- 
tory boilers  of  the  plain  cylindrical  form,  and  continuing  slowly 
heating  them  many  hours,  finally  attaining  temperatures  ex- 
ceeding the  normal  by  15°  F.  (8°. 3  C).  The  investigator  con- 
cludes: 

"  Here  we  have  conclusive  data  suggesting  certain  rules  to 
be  vigorously  adopted  by  all  connected  with  steam-boilers  who 
would  avoid  mysterious  explosions  :  First,  never  feed  one  or 
more  boilers  with  surplus  water  that  has  been  boiled  a  long 
time  in  another  boiler,  but  feed  each  separately.  Second,  when 
boilers  working  singly  or  fed  singly  are  accustomed,  under  high 
pressure,  to  be  worked  for  a  number  of  hours  consecutively, 
day  and  night,  they  should  be  completely  emptied  of  water  at 
least  once  every  week,  and  filled  with  fresh  water.  Third,  in 
the  winter  season  the  feed-water  of  the  boiler  should  be  sup- 
plied from  a  running  stream  or  well  ;  thaw  water  should  never 
be  used  as  feed  for  a  boiler." 

"  Locomotive,  steamboat,  and  stationary  engine  boilers  have 
their  fires  frequently  banked  up  for  hours,  without  feeding  water, 
and  the  steam  fluttering  at  the  safety-valve,  so  as  to  have  them 
all  ready  for  starting  at  a  moment.  This  is  a  dangerous  prac 
tice,  as  the  foregoing  experiments  demonstrate.  While  so 

*  London  Mining  Journal,  June  28,  1856. 


580  THE   STEAM-BOILER. 

standing,  all  the  atmospheric  air  may  be  expelled  from  the 
water,  and  it  may  thereby  attain  to  a  high  heat,  ready  to  gen- 
erate suddenly  a  great  steam-pressure  when  the  feed-pump  is 
set  in  motion.  This  is,  no  doubt,  the  cause  of  the  explosion 
of  many  steam-boilers  immediately  upon  starting  the  engine, 
even  when  the  gauge  indicates  plenty  of  water.  The  remedy 
for  such  explosions  must  be  evident  to  every  engineer — keep 
the  feed-pump  going,  however  small  may  be  the  feed  re- 
quired." 

On  the  other  hand,  the  report  of  a  committee  appointed  by 
the  French  Academy  to  inquire  into  the  superheated-water 
theory  of  steam-boiler  explosions  indicates  at  least  the  difficulty 
of  securing  such  conditions.*  The  committee  constructed  suit- 
able apparatus,  experimented  in  the  most  exhaustive  manner, 
and  investigated  several  explosions  claimed  by  the  advocates  of 
the  theory  to  have  been  due  to  this  cause.  They  failed  to  su- 
perheat water  under  any  conditions  which  could  probably  occur 
in  practice,  and  the  explosions  investigated  were  shown  conclu- 
sively to  have  resulted  from  simple  deterioration  of  the  boilers, 
or  from  carelessness.  It  is  unquestionably  the  fact  that  explo- 
sions due  to  this  cause  are  at  least  exceedingly  rare,  although 
it  is  not  at  all  certain  that  they  may  not  now  and  then  take 
place.  The  ocean  is  constantly  being  traversed  by  thousands 
of  steamers  having  surface-condensers  and  boilers  in  which  the 
water  is  used  over  and  over  again,  and  in  which  every  condition 
is  seemingly  favorable  to  such  superheating  of  the  water ;  but 
no  one  known  instance  has  yet  occurred  of  the  production  of 
this  phenomenon,  there  or  elsewhere,  on  a  large  scale,  where 
boilers  are  in  regular  operation. 

M.  Donny,  who  first  suggested  the  possibility  of  this  action 
as  a  cause  of  boiler-explosions,  has  had  many  followers.  M. 
Dufour,f  who  doubts  if  such  explosions  are  possible  in  the  or- 
dinary working  of  the  boiler,  points  out  the  fact,  however,  that 
boilers  which  are  not  in  operation,  but  which  are  quietly  cool- 
ing down  after  the  working-hours  are  over,  are  peculiarly  well 

*  Annales  de  Mines,  1886. 

f  Sur  1'Ebullition  de  1'Eau,  et  sur  une  cause  probable  d' Explosion  des  Chau- 
dieres  a  Vapeur,  p.  29. 


STEAM-BOILER   EXPLOSIONS.  581 

situated  for  the  development  of  this  form  of  stored  energy.  He 
points  out  the  known  fact  that  many  explosions  have  taken 
place  under  such  conditions,  the  pressure  having  fallen  below 
the  working-pressure.  M.  Gaudry*  makes  the  same  observa- 
tion. Such  cases  are  supposed  to  be  instances  of  "  retarded 
ebullition"  with  decrease  of  pressure  and  superheating  of  the 
water.  Many  circumstances  unquestionably  tend  to  strengthen 
this  view. 

So  tremendous  are  the  effects  of  many  explosions  that  M. 
Audrand  has  expressed  the  belief  that  a  true  explosion  must  be 
preceded  by  pressures  approaching  or  exceeding  200  atmos- 
pheres ;f  an  intensity  of  pressure,  however,  which  no  boiler 
could  approximate.  Mr.  Hall  also  thinks  that  the  shattering 
effect  sometimes  witnessed,  resulting  in  the  shattering  of  a 
boiler  into  small  pieces,  must  be  the  effect  of  a  sudden  and 
enormous  force,  partaking  of  the  nature  of  a  blow  ;;£  and  cites 
cases,  such  as  are  now  known  to  be  common,  of  an  explosion 
taking  place  on  starting  an  engine,  after  the  boiler  has  been  at 
rest  and  making  no  steam  for  a  considerable  time.  M.  Arago 
cites  a  number  of  similar  instances,§  and  Robinson  a  number 
in  still  greater  detail.  ||  Boilers  after  quietly  "  simmering"  all 
night  exploded  at  the  opening  of  the  throttle-valve  or  the 
safety-valve  in  the  morning.  The  locomotive  Wauregan, 
which  exploded  within  sight  and  hearing  of  the  Author  at  Prov- 
idence, R.  I.,  in  February,  1856,  is  mentioned  by  Colburn  as 
such  a  case.  The  engine  had  been  quietly  standing  in  the  en- 
gine-house two  hours,  the  engineer  and  fireman  engaged  clean- 
ing and  packing,  preparatory  to  starting  out.  The  explosion 
was  without  warning  and  very  violent,  stripping  off  the  shell 
and  throwing  it  up  through  the  roof,  and  killing  the  engineer, 
who  was  standing  beside  his  engine. 

Mr.  Robinson^f  thinks  the  usual  cause  of  such  explosions  is 

*  Traite  des  Machines  a  Vapeur. 
f  Comptes  Rendtis,  May,  1855,  p.  1062. 

\  Civil  Engineers'  Journal,  1856,  p.  133;  Dingler's  Journal,  1856,  p.  12. 
§  Annuaire,  1830. 
I  Steam-boiler  Explosions,  p.  62. 
1  Ibid.  p.  66. 


582  THE   STEAM-BOILER. 

the  overheating  of  the  water,  the  phenomenon  being  in  its  ef- 
fects very  like  the  "water-hammer"  in  steam-pipes,  producing 
shocks  which  the  Author  has  shown  to  give  rise  to  instantaneous 
pressures  exceeding  the  working  pressures  ten  or  twenty  times  ; 
the  action  seems,  however,  rather  to  be  that  "boiling  with 
bumping"  familiar  to  chemists  handling  sulphuric  acid  in  con- 
siderable quantities.  Instances  have  been  known  in  which  this 
bumping  has  burst  pipes  or  severely  shaken  boilers  and  setting 
without  producing  explosion. 

The  deaeration  of  water,  and  the  consequent  superheat- 
ing of  the  liquid,  to  which  some  explosions  have  been  attrib- 
uted, are  phenomena  which  have  been  often  investigated.  Mr. 
A.  Guthrie,  formerly  U.  S.  Supervising  Inspector-General  of 
Steam-vessels,  states  that  he  has  made  many  such  experiments,. 
as  follows  :* 

"(i)  In  my  experiments  I  first  procured  a  sample  of  water 
from  the  boiler  of  an  ordinary  condensing-engine  ;  here,  of 
course,  in  addition  to  being  subjected  to  long-continued  boil- 
ing, it  had  passed  through  the  vacuum. 

"  (2)  I  procured  a  sample  from  the  ordinary  high-pressure 
non-condensing  engine-boiler,  which  before  entering  the  boiler 
had  passed  the  heater  at  210°. 

"  (3)  I  procured  some  clean  snow  and  dissolved  it  under  oil, 
so  that  there  was  no  contact  with  the  air. 

"  (4)  I  froze  some  water  in  a  long,  upright  tube,  using  only 
the  lower  end  of  the  ice  when  removed  from  the  tube,  and  dis- 
solved under  oil. 

"  (5)  I  placed  a  bottle  of  water  under  a  powerful  vacuum- 
pump  worked  by  steam,  for  two  hours  ;  agitating  the  water 
from  time  to  time  to  displace  any  air  that  might  possibly  be 
confined  in  it,  then  closed  it  by  a  stop-cock,  so  that  no  air 
could  possibly  return. 

"  (6)  I  boiled  water  in  an  open  boiler  for  several  hours,  and 
filled  a  bottle  half-full,  closed  and  sealed  it  up,  so  that  when  it 
became  cool  it  would  in  effect  be  under  a  vacuum,  agitating  it 
as  often  as  seemed  necessary. 

*  American  Artisan;  Locomotive,  1880. 


STEAM-BOILER   EXPLOSIONS.  583 

"  (7)  Another  bottle  was  filled  with  the  same,  and  sealed. 

"  (8)  I  next  took  some  clean,  solid  ice,  dissolved  it  under 
oil,  and  brought  it  to  a  boil,  which  was  continued  for  an  hour  or 
more,  after  which  it  was  tightly  corked. 

"  (9)  I  procured  a  bottle  of  carefully-distilled  water,  after 
long  boiling  and  having  been  perfectly  excluded  from  air  during 
the  distillation. 

"(id)  I  obtained  a  large  number  of  small  fish,  placed  them 
in  pure,  clean  water  in  an  open-headed  cask,  on  a  moderately 
cold  night,  so  that  very  soon  it  became  frozen  over,  conse- 
quently excluding  the  air,  the  fish  breathing  up  the  air  in  the 
water,  so  that  (if  I  am  correct  in  this  theory)  a  water  freed  from 
air  would  be  the  result ;  but  in  some  of  these  different  processes, 
if  not  in  all,  I  was  likely  to  free  the  water  from  air,  if  it  could 
ever  possibly  occur  in  the  ordinary  course  of  operating  a  steam- 
boiler. 

"  Having  procured  a  good  supply  of  glass-boilers  adapted  to 
my  purpose,  and  so  made  that  the  slightest  changes  could  be 
noted,  and  using  as  delicate  thermometers  as  I  could  obtain,  I 
took  these  samples,  one  after  another,  and  brought  them  to  the 
boiling-point ;  and  every  one,  with  no  variation  whatever,  boiled 
effectually  and  positively  at  212°  Fahrenheit  or  under  ;  nor  was 
there  the  slightest  appearance  of  explosion  to  be  observed." 

This  evidence  is,  of  course,  purely  negative. 

The  superheating  of  water,  on  even  the  small  scale  of  the 
laboratory  experiments  of  Donny,  Dufour,  and  others,  has  never 
been  successfully  performed,  except  with  the  most  elaborate 
precautions.  The  vessel  containing  the  liquid  must  be  abso- 
lutely clean ;  the  washing  of  all  surfaces  with  an  alkaline  solu- 
tion seems  to  be  one  of  the  customary  preliminary  operations. 
The  vessel  must  usually  be  heated  in  a  bath  of  absolutely  uni- 
form temperature  in  order  that  currents  may  not  be  set  up 
within  the  body  of  the  liquid  to  be  heated ;  no  solid  can  be  per- 
mitted to  enter  or  come  in  contact  with  it;  no  shock  can  be  al- 
lowed to  affect  it ;  even  contact  with  a  bubble  of  gas  may  stop 
the  process  of  superheating.  All  these  conditions  are  as  far  re- 
moved as  possible  from  those  existing  in  steam-boilers. 

282.  The  Spheroidal  State,  or Leidenfrost's  phenomenon, 


584  THE   STEAM-BOILER. 

as  it  is  often  called,  is  a  condition  of  the  water,  as  to  tempera- 
ture, precisely  the  opposite  of  that  last  described,  its  tempera- 
ture being  less,  rather  than  greater,  than  that  due  the  pressure ; 
while  the  adjacent  metal  is  always  greatly  overheated,  and  thus 
becomes  a  reservoir  of  surplus  heat-energy  which  can  be  trans- 
ferred at  any  instant  to  the  water.  This  peculiar  phenomenon 
was  first  noted  by  M.  Leidenfrost  about  1746.  It  was  studied 
by  Klaproth,  Rumford,  and  Baudrimont,*  and  more  thoroughly 
by  Boutigny. 

When  a  small  mass  of  liquid  rests  upon  a  surface  of  metal 
kept  at  a  temperature  greatly  exceeding  the  boiling-point  of 
the  liquid  under  the  existing  pressure,  the  fluid  takes  the  form 
of  a  globule  if  a  very  small  mass,  or  of  a  flattened  spheroid  or 
round-edged  disk  if  of  considerable  volume,  and  floats  around 
above  the  metal,  quite  out  of  contact  with  the  latter,  and  grad- 
ually, very  slowly,  evaporates.  The  higher  the  temperature  of 
the  plate,  the  more  perfect  this  repulsion  of  the  liquid.  Should 
the  temperature  of  the  metal  fall,  on  the  other  hand,  the  globule 
gradually  sinks  into  contact  with  it,  and,  at  a  temperature  which 
is  definite  for  every  liquid,  and  is  the  lower  as  it  is  the  more 
volatile,  finally  suddenly  absorbs  heat  with  great  rapidity  and 
evaporates  often  almost  explosively.  If  contact  is  forcibly  pro- 
duced at  the  higher  temperature  of  the  supporting  plate  of 
metal,  as  under  a  blacksmith's  hammer,  a  real  explosion  takes 
place,  throwing  drops  of  the  liquid  in  every  direction. 

M.  Boutigny  found  the  temperature  of  contact  to  be,  for 
water,  alcohol,  and  ether,  respectively,  142°  C.,  134°,  and  61° 
(287°  F.,  273°,  and  142°).  In  all  cases  the  temperature  of  the 
liquid  was  independent  of  that  of  the  metal,  and  somewhat  be- 
low the  boiling-point.  It  is  found,  also,  that  a  real  and  power- 
ful repulsion  is  produced  between  metal  and  liquid;  this  is  sup- 
posed to  be  due,  in  part  at  least,  to  the  cushion  of  vapor  there 
interposing  itself.  Contact  is  accelerated  by  the  introduction 
of  soluble  salts  into  the  liquid. 

It  is  supposed  by  many  writers  that  this  phenomenon  may 
play  its  part  in  the  production  of  explosions  of  steam-boilers, 

*  Ann.  de  Chemie  et  de  Physique,  2d  series,  t.  Ixi. 


STEAM-BOILER   EXPLOSION'S.  585 

and  especially  in  cases  in  which  there  seems  some  evidence  that, 
immediately  before  the  explosion,  there  was  no  apparent  over- 
heating of  the  parts  exposed  to  the  action  of  the  fire,  and  in 
those  still  more  remarkable  instances  in  which  the  shattered 
parts  had  been,  to  all  appearance,  much  stronger  than  other  por- 
tions which  had  not  been  ruptured  ;  no  evidence  existing  of  low- 
water  or  overheating  at  the  furnace,  and  the  pressure  being,  the 
instant  before  the  accident,  at  or  below  its  usual  working  figure. 
Bourne*  has  no  doubt  that  this  does  sometimes  take  place. 
Colburn  gives  a  number  of  instances  of  explosions  taking  place 
under,  apparently,  precisely  such  conditions;  and  Robinsonf 
also  cites  several,  in  some  of  which  the  plates  of  the  shell  were 
badly  shattered,  as  by  a  concussive  force.  In  some  such  in- 
stances evidences  of  overheating,  but  only  far  below  the  water- 
level,  known  to  have  existed  immediately  before  the  explosion, 
have  been  observed,  indicating  repulsion  to  have  there  occurred. 
This  latter  is  simply  still  another  instance  of  bringing  about  the 
same  results  as  when  pumping  water  into  an  overheated  boiler 
in  which  the  water  is  low. 

Mr.  Robinson^  tells  of  a  case  in  which  a  nearly  new  locomo- 
tive, standing  in  the  house,  with  a  pressure,  as  shown  but  a 
moment  before  by  the  steam-gauge,  of  but  40  pounds, — one 
third  its  presumed  safe  working  pressure, — the  fire  low  and  every- 
thing perfectly  quiet,  exploded  with  terrible  violence,  shatter- 
ing the  top  of  the  boiler  directly  over  the  firebox  into  many 
parts.  That  such  explosions  might  occur  were  the  metal  actu- 
ally overheated  under  water,  is  shown  by  experiences  not  at  all 
uncommon. 

In  the  work  of  determining  the  temperatures  of  casting  al- 
loys tested  by  the  Author  §  for  the  United  States  Board  ap- 
pointed in  1875  to  test  iron,  steel,  and  other  metals,  at  the  first 
casting  of  a  bar  composed  of  94.10  copper,  5.43  tin,  while  pouring 
the  metal  into  the  water  for  the  test,  an  explosion  took  place 
which  broke  the  wooden  vessel  which  held  the  water,  and  threw 

*  Treatise  on  the  Steam-engine.  1868. 

f  Steam-boiler  Explosions,  p.  33. 

\  Steam-boiler  Explosions,  p.  62. 

§  Report  on  Copper-tin  Alloys.    Washington,  1879. 


586  THE   STEAM-BOILER. 

water  and  metal  about  with  great  violence.  It  appears  probable 
that  the  metal  was  heated  to  an  unusually  high  temperature,  as 
in  pouring  other  metals  when  at  a  dazzling  white  heat  explo- 
sions sometimes  took  place,  but  they  were  usually  not  violent 
enough  to  do  more  than  make  a  slight  report  as  the  hot  metal 
touched  the  water.  Another  bar  was  cast  at  an  extremely  high 
temperature,  being  at  a  dazzling  white  heat.  On  pouring  a 
small  portion  into  water  in  attempting  to  obtain  the  temperature, 
a  severe  explosion  took  place,  and  this  was  repeated  every  time 
that  even  a  small  drop  of  the  molten  metal  touched  the  water. 
The  cold  ingot-mould  was  then  filled  with  this  very  hot  metaL 
After  the  metal  remaining  in  the  crucible  had  stood  for  several 
minutes  and  had  cooled  considerably,  it  could  be  poured  into 
water  without  causing  the  slightest  explosion.  Thus  it  would 
seem  that  the  temperature  at  which  contact  with  the  water  is 
produced  may  have  an  important  effect  upon  the  violence  with 
which  the  steam  is  generated,  and  that  of  the  explosion  so  pro- 
duced. The  explosions  sometimes  taking  place  with  fatal  effect 
in  foundries  when  molten  metal  is  poured  into  damp  or  wet 
moulds  are  produced  in  the  manner  above  illustrated.  They 
are  usually  apparently  of  the  "fulminating  class."  Another  in- 
stance occurred  within  the  cognizance  of  the  Author,  even  more 
striking  than  either  of  the  above.* 

TAVO  workmen  in  a  gold  and  silver  refinery  were  engaged  in 
"graining"  metal,  which  process  consists  in  pouring  a  small 
stream  of  melted  metal  into  a  barrel  of  water,  while  a  stream  of 
water  is  also  run  into  the  barrel  to  agitate  the  water  already 
there.  Suddenly  an  explosion  occurred  which  literally  shivered 
the  barrel,  and  threw  the  workmen  across  the  room.  Every 
hoop  of  the  barrel,  stout  hickory  hoops,  was  broken.  The 
staves,  seven  eighths  of  an  inch  thick,  and  of  oak,  were  not  only 
splintered,  but  broken  across ;  and  the  bottom,  which  was  resting 
on  a  flat  surface,  and  which  was  of  solid  oak  an  inch  in  thick- 
ness, was  split  and  broken  across  the  grain.  A  box  on  which 
stood  the  man  who  was  pouring  the  metal  was  converted  into 
kindling  wood.  The  metal,  though  scattered  somewhat,  for  the 

*  Reported  in  the  Providence  (R.  I.)  Journal,  Feb.  2,  1881. 


STEAM-BOILER  EXPLOSIONS.  587 

most  part  remained  in  place,  but  the  water  was  thrown  in  all 
directions. 

This  explosion  of  an  open  barrel,  like  the  preceding  cases, 
was  evidently  due  to  the  deferred  thermal  reaction  of  the  water 
with  a  mass  of  very  highly  heated  metal,  with  which  it  was 
finally  permitted  to  come  in  contact  at  a  temperature  which 
allowed  an  explosive  formation  of  steam.  This  class  of  explo- 
sions, by  which  open  vessels  are  shattered  and  the  water  con- 
tained in  them  atomized,  are  by  many  engineers  believed  to 
exemplify  the  terrible  explosions  fulminantes  of  French  writers 
on  this  subject. 

The  temperature  of  maximum  vaporization,  with  iron  plates, 
was  reported  by  the  committee  of  the  Franklin  Institute  to  be 
346^°  F.  (175°  C.)  and  that  of  repulsion  385°  F.  (196°  C.),  and 
to  be  the  same  under  all  pressures.  Any  cause  which  may  retard 
the  passage  of  heat  from  the  iron  to  the  water,  though  but  the 
thinnest  film  of  sediment,  grease,  or  scale,  may  permit  such  in- 
crease of  temperature  as  may  lead  to  repulsion  of  the  water,  the 
overheating  of  the  metal,  the  production  of  the  spheroidal  condi- 
tion, and  the  accidents  due  to  that  phenomenon,  provided  that 
the  fire  be  so  driven  as  to  supply  more  heat  than  can  be  dis- 
posed of  in  ordinary  working  by  the  circulation  and  vapori- 
zation then  going  on.  Robinson's  experiments  with  safety- 
plugs  indicate  that  a  good  circulation  is  usually  a  sufficient 
insurance  against  this  action ;  and  experience  with  the  boilers 
of  locomotives  and  of  torpedo-boats,  in  which  from  50  to  100 
pounds  of  coal  per  square  foot  (244  to  488  kilogs.  on  the  square 
metre)  of  grate  are  burned  every  hour,  shows  that  the  risk,  with 
steam-boilers  of  good  design,  is  not  great.  With  impure  water 
and  defective  circulation  Robinson  observed  many  instances  of 
singular  and  dangerous  phases  of  this  action.*  It  is  suggested 
that  many  explosions  of  locomotives  on  the  road  or  at  stations 
may  be  due  to  the  impact,  on  the  shells  of  their  boilers,  of 
water  thus  projected  from  overheated  iron  below  the  water-line. 
In  many  such  cases  the  engines  have  not  left  the  rails,  the 
break  taking  place  just  back  of  the  smoke-box  or  near  the  fire- 

*  See  his  Steam-boiler  Explosions,  pp.  40-46. 


$88  THE   STEAM-BOILER. 

box,  and  from  the  impact  of  water  thus  thrown  from  the  tube- 
sheets. 

M.  Melsen*  experimentally  proved  it  possible  to  prevent 
the  occurrence  of  the  spheroidal  condition  by  the  distribution 
of  spurs  or  points  of  iron  over  the  endangered  sheets. 

The  conductivity  of  the  metal  has  an  important  influence  on 
the  effect  of  contact,  suddenly  produced,  between  the  red-hot 
solid  and  the  liquid.  Professor  Walter  R.  Johnson  observed,  in 
his  elaborate  experiments,f  that  brass  produced  much  greater 
agitation  of  the  water  when  submerged  at  the  red  heat  than  did 
iron.  He  also  noted  the  singular  fact  that  water  at  the  boiling- 
point,  thrown  upon  red-hot  iron,  requires  more  time  for  evapo- 
ration than  cold  water,  probably  in  consequence  of  the  greater 
efficacy  of  the  latter  in  bringing  down  the  temperature  of  the 
metal  to  that  of  maximum  rapidity  of  action.  The  contact 
with  the  iron  of  incrustation,  oxide,  or  other  foreign  matter  ac- 
celerated this  process  also.  Johnson  found  that  beyond  the 
temperature  of  maximum  repulsion  vaporization  was  acceler- 
ated by  further  elevation  of  temperature. 

At  the  meeting  of  the  British  Association  in  1872,  Mr.  Bar- 
rett read  a  paper  upon  the  conditions  affecting  the  spheroidal 
state  of  liquids  and  their  possible  relationship  to  steam-boiler 
explosions.  The  presence  of  alkalies  or  soaps  in  water  percep- 
tibly aids  in  the  production  of  the  spheroidal  state.  A  copper 
ball  immersed  in  pure  water  produced  a  loud  hissing  sound  and 
gave  off  a  copious  discharge  of  steam.  On  adding  a  little  soap 
to  the  water  the  ball  entered  the  liquid  quietly.  Albumen, 
glycerine,  and  organic  substances  generally  produced  the  same 
result.  The  best  method  is  to  use  a  soap  solution,  and  to  plunge 
into  this  a  white-hot  copper  ball  of  about  two  pounds  weight. 
The  ball  enters  the  liquid  quietly,  and  glows  white  hot  at  a 
depth  of  a  foot  or  more  beneath  the  surface.  Even  against 
such  pressure  the  ball  will  be  surrounded  with  a  shell  of  vapor 
of  an  inch  in  thickness.  The  reflection  of  the  light  from  the 
bounding  surfaces  of  the  vapor-bubble  surrounding  the  glowing 


*  Bull,  de  1'Academie  Royale  de  Belgium,  April,  1871. 
f  Reports  on  Steam-boilers,  H.  R.,  1832,  p.  in. 


STEAM-BOILER  EXPLOSIONS,  589 

ball  gives  to  the  envelope  the  appearance  of  burnished  silver. 
As  the  ball  gradually  cools,  the  bounding  envelope  becomes 
thinner,  and  finally  collapses  with  a  loud  report  and  the  evolu- 
tion of  large  volumes  of  steam.  Mr.  Barrett  makes  the  sugges- 
tion that  the  traces  of  oil,  or  other  organic  matters  which  find 
their  way  into  a  steam-boiler,  may  similarly  produce  a  sudden 
generation  of  steam  sufficient  to  acco'unt  for  certain  problemati- 
cal explosions,  and  thus  lends  some  strong  confirmatory  evidence 
to  the  idea  often  promulgated  by  others  within  and  without  the 
engineering  profession. 

283.  Steady  Rise  in  Pressure  has  been  shown  by  the 
experiments  of  the  committee  of  the  Franklin  Institute,  and 
by  numerous  cases  of  explosion,  both  before  and  since  their 
time,  to  be  capable  of  producing  very  violent  explosions.  In 
such  cases,  the  steam  being  formed  more  rapidly  than  it  is 
given  exit,  the  pressure  steadily  increases  until  a  limit  is  found 
in  the  final  rupture  of  the  weakest  part  of  the  boiler.  Should 
this  break  occur  below  the  water-line,  and  be  the  result  of  long 
decay  or  injury,  no  explosion  may  ensue ;  but  should  the  rup- 
ture be  extensive,  or  should  it  occur  above  or  near  the  surface 
of  the  water,  the  succession  of  phenomena  described  by  Clarke 
and  Colburn  may  follow,  and  an  explosion  of  greater  or  less 
violence  may  take  place.  The  intensity  of  the  effect  will  de- 
pend largely  upon  the  quantity  of  stored  energy  liberated,  and 
partly  upon  the  suddenness  with  which  it  is  set  free.  A  slowly- 
ripping  seam  or  gradually  extending  crack  would  permit  a 
far  less  serious  effect  than  the  general  shattering  of  the  shell, 
or  an  instantaneously  produced  and  extensive  rent. 

The  time  required  to  produce  a  dangerous  pressure  is  easily 
calculated  when  the  weight  of  water  present,  W,  the  range  of 
temperature  above  the  working  pressure  and  temperature, 
^  —  tv  and  the  quantity  of  heat,  Q,  supplied  from  the  furnace 

'are  known,  and  is 

W(t°-t° 

Q~ 

Professor  Trowbridge  gives  the  following  as  fair  illustrations 
of  suoh  cases  :* 

*  Heat  as  a  Source  of  Power,  p.  191. 


59O  THE   STEAM-BOILER. 

(i)  A  marine  tubular  boiler  is  of  the  largest  size,  such  that 
W  —  79,000  Ibs.  of  water. 

Suppose  the  working  pressure  to  be  2\  and  the  dangerous 
pressure  4  atmospheres. 

The  boiler  contains  5000  square  feet  of  heating-surface  ; 
and  supposing  the  evaporation  to  be  3  Ibs.  of  water  per  hour 
for  each  square  foot,  we  shall  have,  taking  1000  units  of  heat 
as  the  thermal  equivalent  of  the  evaporation  of  I  Ib.  of  water, 

/,  -  t  =  29°  F. 
5000  X  3  X  1000 


79,000  X  29 
T= 


5000X3XIOOQ 
60 

(2)  A  locomotive  boiler,  containing  5000  Ibs.  of  water,  hav- 
ing 1  1  square  feet  of  grate-surface,  and  burning  60  Ibs.  of  coal 
per  hour  on  each  square  foot  of  grate,  each  pound  of  coal 
evaporates  about  7  Ibs.  of  water  per  hour,  making  77  Ibs.  of 
water  evaporated  per  minute. 

Suppose  the  working  pressure  to  be  90  Ibs.,  and  the  danger- 
ous pressure  to  be  -175, 


5000  X  50 

1  =  -----  =  s*  minutes. 
77  —  looo 

(3)  The   Steam  Fire-engine.  —  The  boiler  contains  338  Ibs. 
of  water  and   157   square  feet  of  heating-surface.     Supposing 
each   square  foot  of  heating-surface   to  generate  but    I   Ib.  of 
steam  in  one  hour,  the  pressure  will  rise  from  100  to  200  Ibs.  in 

T  =  7  minutes. 

(4)  To  find,  in  the  same  boiler,  how  long  a  time  will  be  re- 
quired to  get  up  steam;  that  is,  to  carry  the  pressure  to  100  Ibs. 


STEAM-BOILER  EXPLOSIONS.  59 1 

If  we  suppose  but  ii  cubic  feet  of  water  in  the  boiler,  we  shall 
have 

rr         93  X  117 

T=  - —      .          =4.1  minutes. 
I57X  IOQO 

60 

Thus,  if  IV  is  diminished,  the  time  T  is  diminished  in  the 
same  proportion.  The  lowering  of  the  water-level  from  failure 
of  the  feed-apparatus  increases  the  danger,  not  only  by  expos- 
ing plates  to  overheating,  but  by  causing  a  more  rapid  rise  of 
pressure  for  a  given  rate  of  combustion. 

Gradual  increase  of  pressure  can  never  take  place  if  the 
safety-valve  is  in  good  order,  and  if  it  have  sufficient  area. 

The  sticking  of  the  safety-valve,  either  of  its  stem  or  its 
seat,  the  bending  of  the  stem  or  the  jamming  of  the  valve  by 
a  superincumbent  object  or  lateral  strains,  and  similar  accidents, 
have  produced,  where  boilers  were  strong  and  otherwise  in 
good  order,  some  of  the  most  terrific  explosions  of  which  we 
have  record.  The  parts  of  the  boiler  have  been  thrown  enor- 
mous distances,  and  surrounding  buildings  and  other  objects 
levelled  to  the  ground,  while  the  report  has  been  heard  miles 
away  from  the  scene  of  the  disaster. 

The  records  of  the  Hartford  company  up  to  1887  include 
accounts  of  26  explosions  of  vessels  detached  from  the  generat- 
ing boiler,  used  at  moderate  pressures  for  various  purposes  in 
the  arts,  and  there  have  been  many  others  of  less  importance 
that  were  not  considered  worthy  of  public  mention.  It  is  con- 
cluded that  the  percentage  of  explosions  among  bleaching, 
digesting,  rendering,  and  other  similar  apparatus  is  ten  times 
greater  than  among  steam-boilers  at  like  average  pressures,  and 
the  destructive  work  done  is  quite  as  astonishing  as  that  by  the 
explosion  of  ordinary  steam-generators.* 

This  is  sufficiently  decisive  of  the  question  whether  it  is 
possible  to  produce  destructive  explosions  of  boilers  simply  by 
excess  of  pressure  above  that  which  the  vessel  is  strong  enough 
to  withstand.  In  these  cases  low-water  and  all  the  other 
special  causes  operating  where  fire  and  high  temperatures  exist, 

*  The  Locomotive,  1887. 


592  THE   STEAM-BOILER. 

and  such  absurd  theories  as  the  generation  of  gas  or  the  action 
of  electricity,  are  eliminated  ;  and  it  is  seen  that  mere  deteri- 
oration and  loss  of  strength,  or  a  rise  of  steam-pressure,  even 
where  there  is  an  ample  supply  of  water,  may  produce  explo- 
sions of  the  utmost  violence. 

284.  The  Relative  Safety  of  Boilers  of  the  various  types 
is  determined  mainly  by  their  general  design,  and  their  greater 
or  less  liability  to  serious  and  extensive  injury  by  the  various 
accidents  and  methods  of  deterioration  to  which  all  are  to  a 
greater  or  less  extent  liable.  The  two  essential  principles  by 
which  to  compare  and  to  judge  the  safety  of  boilers  are : 

(1)  Steam-boilers  should  be  so  designed,  constructed,  oper- 
ated, inspected,  and  preserved  as  not  to  be  liable  to  explosion. 

(2)  Boilers  should  be  so  designed  and  constructed  that,  if 
explosive  rupture  occurs  at  all,  it  shall  be  with  a  minimum  of 
danger  to  attendants  and  surrounding  objects. 

The  prevention  of  liability  to  explosion,  and  the  provision 
against  danger  should  explosion  actually  take  place,  are  the  two 
directions  in  which  to  look  for  safety. 

As  Fairbairn  has  remarked,  the  danger  does  not  consist  in 
the  intensity  of  the  pressure,  but  in  the  character  and  construc- 
tion of  the  boiler.*  Other  things  being  equal,  the  boiler,  or 
that  form  of  boiler  in  which  the  original  surplus  strength  of 
form  and  of  details  is  greatest,  and  which  is  at  the  same  time 
best  preserved,  is  the  safest.  That  class  in  which  original 
strength  is  most  certainly  and  easily  preserved  has  an  impor- 
tant advantage ;  those  boilers  in  which  facilities  for  constant 
oversight,  inspection,  and  repairs  are  best  given  are  superior  in 
a  very  important  respect  to  others  deficient  in  those  points. 
For  example,  the  cylindrical  tubular  boiler,  if  properly  set,  is 
very  accessible  in  all  parts,  and  may  be  at  all  times  examined : 
it  offers  peculiar  facilities  for  inspection  and  the  hammer-test, 
and  can  be  readily  kept  in  repair ;  but  it  is  liable,  in  case  of  its 
becoming  weakened  by  corrosion  over  any  considerable  area 
or  along  any  extended  line  of  lap,  to  complete  disruptive  ex- 
plosion. 

*  Engineering  Facts  and  Figures,  1865. 


STEAM-BOILER  EXPLOSIONS.  593 

On  the  other  hand,  the  various  "  sectional,"  or  so-called 
<c  safety,"  boilers  are  rarely  as  convenient  of  access  or  of 
inspection,  and  cannot  usually  be  as  readily  and  completely 
cleaned ;  but  they  are  so  designed  and  constructed  as  to  be 
little,  if  at  all,  liable  to  dangerous  explosive  rupture,  and  if  a 
tube  or  other  part  bursts  it  is  not  likely  to  endanger  life  or 
property.  That  boiler  is,  therefore,  on  the  whole,  best  which 
is  least  liable  to  those  kinds  of  injury  which  lead  to  explosion, 
and  which  is  least  likely  to  do  serious  harm  should  explosion 
actually  take  place.*  Those  who  select  the  tubular  boiler  are 
commonly  influenced  mainly  by  considerations  of  cost  and  the 
first  of  the  above  considerations ;  while  the  users  of  the  water- 
tube  sectional  boiler  are  controlled  by  the  second,  in  so  far  as 
either  considers  this  form  of  risk  at  all. 

During  the  experiments  of  Jacob  Perkins,  about  1825  and 
later,  the  value  of  the  "  sectional "  boilers,  where  high-pressures 
are  adopted,  was  well  shown.  He  frequently  raised  his  steam- 
pressure  to  100  atmospheres,f  and  in  his  earlier  work  rupture 
often  took  place,  but  no  ill  effects  followed.  The  division 
of  the  boiler  into  numerous  compartments  saved  the  attendants 
from  injury.  In  a  letter  to  Dr.  T.  P.  Jones,  dated  March  8, 
18274  Mr.  Perkins  states  that  he  had  worked  at  the  above- 
mentioned  pressure  with  a  ratio  of  expansion  of  12  ;  his  usual 
pressure  wras  about  two  thirds  that  amount,  and  the  ratio  of 
expansion  8.  Mr.  Perkins  was  then  building  an  engine  to 
safely  carry  a  pressure  of  2000  pounds  per  square  inch.§ 

285.  Defective  Designs,  causing  explosion,  are  not  as 
common  as  many  other  causes.  They  exist,  however,  more 
frequently  than  is  probably  usually  supposed.  The  defects  are 
generally  to  be  observed  in  the  staying  of  such  boilers  as  re- 
quire bracing;  in  the  insertion  of  the  heads  of  plain  cylindrical 
boilers;  in  the  attachment  of  drums,  and  the  arrangement  of 

*  Dr.  E.  Alban,  following  John  Stevens,  was  probably  the  first  to  enunciate 
the  principle,  "  so  construct  the  boiler  that  its  explosion  may  not  be  dangerous." 
The  High-pressure  Steam-engine,  1847,  p.  70. 

f  Jour.  Franklin  Inst.,  vol.  iii.,  p.  415. 

\  Ibid.,  p.  412. 

§  Reports  on  Steam-boilers,  H.  R.,  1832,  p.  188. 
33 


594 


THE   STEAM-BOILER. 


man-holes  and  hand-holes ;  and,  less  frequently,  in  the  selection 
of  the  proper  thickness  and  quality  of  iron  for  shells  and  flues. 
Such  defects  as  these  are  the  most  serious  possible  ;  they 
are  not  only  serious  in  themselves  and  at  the  start,  but  are 
of  a  kind  which  is  commonly  very  certain  to  be  exaggerated, 
and  rendered  continually  more  dangerous  with  age.  A  thin 
shell  grows  constantly  thinner,  a  weak  stay  or  brace  weaker, 
and  an  unstayed  head  more  likely  to  yield  every  day ;  while  a 
flue  originally  too  thin  is  all  the  time  overstrained,  not  simply 
by  the  steam-pressure,  but  also  by  the  action  of  the  relatively 
stronger  parts  around  it.  The  most  minute  study  of  every 
detail  and  the  most  careful  calculation  of  the  strength  of  every 
part,  with  an  allowance  of  an  ample  factor  of  safety,  are  the 
essentials  to  safety  in  design. 

Faulty  design  in  bracing  is  illustrated  by  an  explosion  which 
took  place  in  New  York  City,  January  15,  1881,  by  which,  for- 
tunately, however,  no  loss  of  life  was  caused.  A  dome-head, 
proportioned  and  braced  as  shown  in  the  next  figure,  was  blown 
out  and  tore  up  a  sidewalk,  under  which  the  boiler  was  set, 


K 


E      A 


FIG.  133.— DOME  AND  HEAD. 

doing  no  other  damage.      The    case  was   examined    by    Mr. 
Rose,  who  reported  substantially  as  follows : 

The  dome-crown  tearing  around  the  edge  at  A,  also  tore 
across  at  J3,  being  thus  completely  severed.  The  iron  at  the 
fractures  was  of  excellent  quality.  The  plate  showed  lamina- 
tion in  places,  and  the  crack  around  A  was  rusty,  and  evidently 


STEAM-BOILER   EXPLOSIONS.  595 

not  of  recent  formation.  The  six  stays,  three  of  which  are 
shown  in  place  at  C,  Fig.  133,  were  all  in  position  in  the  dome, 
and  their  surfaces  of  contact  with  the  dome  were  covered  by  a 
black  polish,  indicating  movement  and  abrasion. 


FIG.  134.— EXPLOSION  OF  DOME. 


Apparently,  as  the  pressure  and  temperature  increased  and 
decreased  the  dome-head  might  lift  and  fall,  bending  on  A  as  a 
centre ;  thus,  taking  /  as  a  centre,  the  movement  of  C  would 


FIG.  135.— DEFECTIVE  FORM. 

be  in   the  direction  of  F,  while  at  D  the  direction  would  be 
toward  /,  and  the  direction  of  motion  of  the  two  would  nearly 


THE   STEAM-BOILER. 

coincide.  The  exploded  dome  shows  an  indentation  at  /,  due 
to  the  motion  of  the  foot  of  the  stay. 

Another  error  in  the  design  of  this  boiler  is  that  the  diameter 
of  the  dome-shell  is  34  inches,  and  a  circle  of  iron  about  18  inches 
in  diameter  is  punched  out  of  the  shell  at  D.  This  opening  is 
required  only  to  admit  an  inspector  or  workman  to  the  interior 
of  the  boiler ;  hence  it  is  several  inches  wider  than  it  should  be. 

Defective  design  is  illustrated  in  the  case  of  the  next  boiler, 
the  explosion  of  which  left  it  in  the  form  shown  in  Fig.  135.* 

This  boiler  consisted  of  two  incompletely  cylindrical  shells, 
united  as  in  the  next  figure,  and  ineffectively  stayed  at  the 

\  /  lines  of  contact.     This  is  a  form  which, 

/•  '  "  '  11  insufficiently  braced,  becomes  peculiarly 

\  dangerous.  In  the  case  illustrated,  the 
FIG.  i36.-juNCTioN  OF  SHELLS,  braces  yielded,  after  having  been  weak- 
ened by  continual  alteration  of  form,  and  split  the  two  shells 
apart  as  seen.  It  is  probably  possible  to  brace  boilers  of  this 
type  safely,  but  it  is  better  to  avoid  their  use.  They  have  some- 
times been  used  for  marine  purposes,  where  lack  of  space  com- 
pelled special  expedients,  the  bracing  consisting  of  strong  bolts 
with  nuts  and  washers  on  the  outside  of  the  shell — a  compara- 
tively strong  and  safe  construction. 

Steam-domes  are  a  source  of  some  danger  and  of  additional 
expense,  however  well  designed  and  attached  ;  and  it  is  proba- 
bly good  economy,  all  things  considered,  to  dispense  with  them 
altogether,  using  a  dry  pipe  instead,  and  expending  the  amount 
of  their  extra  cost  on  an  increase  in  size  of  boiler  over  that 
which  would  have  otherwise  been  selected.  The  large  boiler 
will  steam  easier  and  more  regularly,  will  give  drier  steam,  and 
will  be  less  liable  to  danger  of  deterioration  or  of  explosion. 
A  steam-drum  above  the  boiler  and  connected  by  two  separate 
nozzles,  or  a  drum  connecting  the  several  boilers  of  a  battery, 
is  not  subject  to  the  objections  which  apply  to  the  attached 
dome. 

286.  Defective  Construction,,  material,  and  workmanship 
are  responsible  for  many  explosions  of  steam-boilers.  Thin, 

*  Locomotive,  Feb.  1880. 


STEAM-BOILER   EXPLOSIONS.  597 

laminated,  or  blistered  sheets,  imperfect  welds  in  bracing,  the 
strain  produced  by  the  drift-pin,  carelessness  in  the  attachment 
of  nozzles  and  drums,  and  in  neglect  of  the  precaution  of 
strengthening  man-holes  and  hand-holes,  and  bad  riveting,  are 
all  common  causes  of  weakness  and  accidents.  Only  the  most 
careful  and  skilful,  as  well  as  conscientious,  builders  can  be  re- 
lied upon  to  avoid  all  such  faults,  and  to  turn  out  boilers  as 
strong  and  safe  as  the  designs  may  permit. 

In  all  cases,  careful  and  unintermitted  inspection  by  an  ex- 
perienced, competent,  and  trustworthy  inspector  should  be 
provided  for  by  the  proposing  purchaser  and  user  of  the  boiler. 
In  the  case  of  some  of  the  more  modern  forms  of  boiler,  con- 
structed under  a  system  of  manufacture  which  includes  some 
machine  fitting  and  working  to  gauge  of  interchangeable  parts, 
with  regular  inspection  before  assemblage,  this  supervision  be- 
comes less  essential,  and  a  careful  test  and  trial,  previous  to 
acceptance,  may  be  all  that  is  necessary  to  insure  a  satisfactory 
and  safe  construction.  Wherever  defective  material  or  bad 
workmanship  is  detected,  the  fault  should  always  be  corrected 
before  the  boiler  is  accepted,  and  previous  to  any  trial  or  use 
under  steam.  Careless  riveting  and  the  use  of  the  drift-pin  are 
defects  which  cannot  often  be  readily  detected  afterward,  and 
they  are  such  common  causes  of  explosion  that  too  much  care 
cannot  be  taken  to  avoid  any  establishment  of  which  the  repu- 
tation in  this  regard  is  not  the  best. 


FIG.  137. — DEFECTIVE  WELDING. 

Defective  welds,  the  cause  of  many  unfortunate  accidents 
following  the  yielding  stays  or  braces,   are   among  the  most 


THE   STEAM-BOILER. 

common  and  least  easily  detected  of  all  faults.  They  are  due 
to  the  difficulty  of  producing  metallic  contact  in  abutting  sur- 
faces between  which  particles  of  scale  and  superficial  oxidation 
may  interpose.  The  grain  of  the  iron,  as  illustrated  in  the  ac- 
companying engraving,  is  broken  at  such  junctions,  and  it  is 
difficult  to  secure  a  good  weld,  and  next  to  impossible  to  de- 
termine until  it  actually  breaks  whether  it  is  seriously  un- 
sound. 

Defective  workmanship  is  often  exhibited  most  strikingly 
by  the  distorted  forms  of  rivets,  revealed  after  explosion  has 
caused  a  fracture  along  the  seam,  or  when  the  yielding  of  the 
weakened  seam  has  resulted  in  an  explosion.  The  following 
illustrations  of  a  variety  of  cases  of  such  distortion,  all  taken 
from  a  single  boiler,*  show  how  very  serious  this  kind  of  de- 
fect may  be.  It  is  not  to  be  presumed  that  such  carelessness 
or  worse,  as  is  here  exemplified,  is  to  be  attributed  to  the 
builder  himself,  but  rather  to  the  fault  of  workmen  carefully 
concealing  their  action  from  the  eye  of  the  foreman  or  inspec- 
tor. No  law  or  rule  can  protect  the  purchaser  from  this  kind 
of  fault ;  his  only  reliance  must  be  upon  the  reputation  of  the 
maker  and  his  workmen,  and  the  vigilance  and  skill  of  his  in- 
spector. 

FlG.  138. — Rivet  "  driven"  in  overset  holes,  the  conical 
point  broken  off  by  the  tearing  apart  of  the  plates,  the  head 


FIG.  138.  FIG.  139. 

nearly  severed    from    the  body,  and    probably  weakened    in 
"  driving." 

FlG.    139. — Rivet  "driven"  in  overset  holes,  head  broken 
off  by  the  tearing  apart  of  the  plates,  conical  point  also  nearly 

*  Locomotive,  Feb.  1880. 


S  TEA  M-B  OILER  EX  PL  OSIONS. 


599 


broken  off,  bad  sample  of  "  driving,"  cone  too  flat  to  properly 
hold  down  the  plate. 

The  next  figure  illustrates  a  group  of  similar  distorted  riv- 
ets which  played  their  part  in  the  production  of  an  explosion. 


FIG.  140. — DEFECTIVE  RIVETS. 


FlG.  141. — Rivet  "driven"  in  slightly  overset  holes,  point 
excentric  and  not  symmetrical,  too  flat  to  properly  secure  the 
edge  of  the  plate. 

FlG.  142. — Rivet  "  driven"  in  badly  overset  holes,  very  weak. 


FIG.  141. 


PIG.  142. 


See  Figs.  143,  144,  145,  which  were  "sheared"  at  the  time  of 
the  explosion.  The  dark  shading  on  lower  end,  Fig.  142,  indi- 
cates an  old  crack. 

FlGS.  143,  144,  145. — Samples  selected  from  a  number  taken 
from  a  "  sheared  "  seam,  which  was  believed  to  be  the  initial 
break  from  which  the  explosion  arose.  They  were  no  doubt 
similar  to  Fig.  142  before  they  gave  way. 


6OO  THE   STEAM-BOILER. 

The  Author,  on  one  occasion,  picked  out  with  his  fingers 


FIG.  143. 


FIG.  144. 


FIG.  145. 


twelve  consecutive  rivets,  deformed  like  those  here  illustrated, 
from  a  torn  seam  in  an  exploded  boiler. 


FIG.  146. 

FlG.  146. — Rivet  "  driven"  in  overset  holes  ;  it  was  probably 
fractured  under  the  head  in  driving.  Taken  from  a  seam  that 
was  broken  through  the  rivet-holes. 


FIG. 


FIG.  148. 


FlGS.  147  and  148. — Long  rivets  taken  from  a  broken  casting 
which  they  were  intended  to  secure  to  the  wrought-iron  head 


STEAM-BOILER  EXPLOSIONS.  6oi 

of  the  boiler.  The  holes  in  the  wrought-iron  plate  were 
"  drifted  "  and  chipped  to  allow  the  rivets  to  enter,  as  shown 
by  the  enlarged  portion  of  the  body.  This  irregular  upsetting 
and  the  sharp  little  wave  of  iron  on  the  body  of  Fig.  147  indi- 
cate the  thickness  of  the  wrought-iron  plate. 

287.  Developed  Weakness,  usually  a  consequence  of 
progressing  decay  by  corrosion,  is  the  most  common  of  all 
causes  of  the  explosion  of  steam-boilers.  A  boiler,  designed  and 
constructed  of  the  best  possible  proportions  and  of  the  best  of 
materials,  having  at  the  start  a  real  factor  of  safety  of  six, 
may  be  assumed  to  be  as  safe  against  this  kind  of  accident  as 
possible  ;  but  with  the  beginning  of  its  life  decay  also  begins, 
and  the  original  margin  of  safety  is  continually  lessened  by  a 
never-ceasing  decay.  The  result  is  an  early  reduction  of  this 
margin  to  that  represented  by  the  difference  between  the  work- 
ing pressure  and  that  fixed  as  a  maximum  by  the  inspector's 
tests.  Should  this  difference  be  sufficient  to  insure  against  ac- 
cident resulting  from  further  depreciation  in  the  interval  be- 
tween inspector's  or  other  tests,  explosion  will  not  occur ; 
should  this  margin  not  be  sufficient,  danger  is  always  to  be  ap- 
prehended, and  almost  a  certainty  that  rupture,  and  possibly 
explosive  rupture,  will  at  some  time  occur.  This  margin  is, 
legally,  usually  fifty  per  cent  ;  it  is  too  small  to  permit  the  pro- 
prietor to  feel  a  real  security.  It  is  usually  thought  that  the 
tests  should  show  soundness  under  pressures  at  least  double 
the  regular  working  pressure  at  which  the  safety-valve  is  set.* 
Many  cases  have  been  known  in  which  the  boiler  has  yielded 
at  the  working  pressure  not  very  long  after  the  regular  official 
inspection  and  pressure-test  had  taken  place. 

Such  an  example  was  that  of  the  explosion  of  the  boiler  of 
the  Westfield,  in  New  York  Harbor,  in  June,  1871. 

The  steam  ferry-boat  Westfield  is  one  of  three  boats  which 
have  formed  one  of  the  regular  lines  between  New  York  and 
Staten  Island.  The  Westfield  made  her  noon  trip  up  from 

*  Experiments  made  by  the  Author,  and  later  by  other  investigators,  have  in- 
dicated the  possibility  that  an  apparent  factor  of  safety  of  two,  under  load  momen- 
tarily sustained,  may  not  actually  mean  a  factor  exceeding  one  for  permanent 
loading.—"  Materials  of  Engineering,"  vol.  i.,  §  133;  vol.  ii.,  §  295. 


6O2  THE   STEAM-BOILER. 

the  island  to  the  city  on  Sunday,  July  3Oth,  and  while  lying  in 
the  New  York  slip  her  boiler  exploded,  causing  the  death  of 
about  one  hundred  persons  and  the  wounding  of  as  many 
more. 

The  boiler  is  of  a  very  usual  form,  as  represented  in  Fig. 
149,  and  is  known  as  a  "  marine  return-flue  boiler." 

The  diameter  of  its  shell — the  cylindrical  part  was  ruptured 
—is  ten  feet ;.  its  thickness,  No.  2  iron,  twenty-eight  hundredths 
inch. 


FIG.  149. — BOILER  OF  THE  WESTFIELD. 

The  evidence  indicated  that  the  explosion  occurred  in  con- 
sequence of  the  existence  of  lines  of  channelling  and  long-exist- 
ing cracks,  by  which  the  boiler  was  gradually  so  weakened  that, 
six  weeks  after  its  inspection  and  test,  the  pressure  of  steam 
being  allowed  by  the  engineer  to  rise  slightly  above  the  pres- 
sure allowed,  the  boiler  was  ruptured,  giving  way  along  a 
horizontal  seam  and  tearing  a  course  out  of  the  boiler. 

The  common  lap-joint  customarily  adopted  in  the  construc- 
tion of  boilers  is  liable  to  such  serious  distortion  under  very 
heavy  pressures  as  to  produce  leakage  before  actually  yielding, 
and  this  leakage  is  sometimes  so  great  as  to  act  as  a  safety- 
valve.  Thus,  suppose  a  straight  strip  of  plate  riveted  up  in 
parts  as  in  Fig.  150.*  A  heavy  pull  will  cause  distortion  as 
shown,  in  all  cases  except  where  a  butt-joint  is  made  with  a 
covering  strip  on  each  side.  If  the  metal  is  brittle  and  the 
rivet-heads  strong,  preventing  the  bending  of  the  plate  on  the 

*  See  Locomotive,  Oct.  1880. 


STEAM-BOILER  EXPLOSIONS. 


603 


line  of  rivet-holes,  the  plate  will  probably  break  adjacent  to  G 
or  F,  Fig.  150;  or  in  the  middle,  /  and  H.  But  should  the 
plates  be  ductile  or  the  rivet-heads  weak,  the  break  would  occur 
at  the  line  through  the  holes. 


B 


If  the  plates,  Fig.  150,  A,  etc.,  were  straight  at  the  joint, 
the  extreme  end,  L,  must  contract  and  the  outer  one  expand  at 
M,  involving  in  the  one  a  compression  or  upsetting,  and  in  the 
other  drawing  the  metal.  If  the  joint  be  a  butt,  with  a  single 
outer  cover,  C,  a  similar  contraction  must  take  place  at  both  ends, 
and  a  contraction  of  the  middle  of  the  covering  strip,  while  the 
opposite  would  take  place  in  the  case  of  the  joint  with  the  inner 
cover,  B.  These  distortions  are  not  likely  to  take  place  in  a 
transverse  seam  of  a  cylindrical  boiler-shell  from  internal  pres- 
sure. The  butt-joint,  with  two  covering  plates,  £,  would  re- 
tain its  shape. 

Lapped  longitudinal  joints  are  shown  at  A'.  Single-riv- 
eted and  single-covered  butts  at  B'  and  C.  D'  shows  a  double- 
riveted,  single-covered  butt.  The  next  figures  (151,  152)  show 


FIG.  151. 


~~f L  p  ~    L 

Before  Stretching.  After  Stretching. 

FIG.   152. 


the  effect   of  strain  on   rivet-holes  and  on  holes  filled  by  the 
rivet. 

Multiple  explosions  are  not  infrequent.  They  usually  occur 
in  consequence  of  the  explosion  of  one  of  a  battery,  with  the 
result  of  injuring  adjacent  boilers  in  such  manner  that  they  also 


604  THE   STEAM-BOILER. 

explode,  the  phenomena  following  each  other  so  quickly  as  to 
produce  the  appearance  of  simultaneous  explosion.  It  is  pos- 
sible also  that  in  some  cases  an  accession  of  pressure  in  a  set 
of  boilers  may  take  place  with  such  suddenness  as  to  explode 
several,  notwithstanding  there  may  exist  a  difference  in  their 
resisting  power,  the  weakest  not  being  given  time  to  act  as  a 
safety-valve  to  the  rest.  It  is  doubtful,  however,  whether  such 
cases  can  often  if  ever  arise. 

288.  General  and  Local  Decay  introduce  vastly  different 
degrees  and  elements  of  danger.  As  has  been  elsewhere  stated, 
in  effect,  an  explosion  comes  of  extended  rupture ;  while  local 
injuries  or  breaks,  if  they  do  not  lead  to  wider  injury,  cannot 
cause  widespread  disaster.  Hence,  general  corrosion,  extend- 
ing over  considerable  areas  of  plate  or  along  lines  of  considera- 
ble length,  is  a  cause  of  danger  of  complete  disruption  and  ex- 
plosion. A  corroded  spot  in  a  firebox,  a  loosened  rivet,  or 
even  a  broken  stay,  if  the  boiler  be  otherwise  well  proportioned, 
well  built,  and  in  good  order,  may  not  be  a  serious  matter;  but 
a  thinned  sheet  in  the  shell,  a  long  groove  under  a  lap,  a  line 
of  loose  rivets,  or  a  cluster  of  weakened  stays  or  braces,  will 
certainly  be  most  dangerous.  General  or  widespread  corrosion 
is  very  liable  to  lead  to  explosion  ;  local  and  well-guarded  cor- 
rosion may  cut  quite  through  the  metal,  and  simply  cause  a 
leak  or  an  unimportant  "  burst."  Old  fireboxes  are  often  seen 
covered  with  "  patches"  in  places,  and  yet  they  very  rarely  ex- 
plode. Such  a  state  of  affairs  may,  nevertheless,  by  finally 
producing  large  areas  of  patched  and  fairly  uniformly  weak 
portions  of  the  boiler,  lead  to  precisely  the  conditions  most 
favorable  to  explosion.  A  steam-boiler  experimentally  ex- 
ploded at  Sandy  Hook,  N.  J.,  September,  1871,*  had  previ- 
ously, by  repeated  rupture  by  hydraulic  pressure  and  patching, 
been  gradually  brought  into  precisely  this  state,  and  exploded 
under  steam  at  53^  pounds, — about  four  atmospheres  pressure, — 
a  slightly  lower  pressure  than  it  had  sustained  (59  pounds)  at  its 
last  test.  On  this  occasion,  when  a  pressure  was  reached  of 
50  pounds  per  square  inch,  a  report  was  heard  which  was  prob- 

*  Journal   Franklin  Institute,  January,  1872. 


STEAM-BOILER  EXPLOSIONS.  605 


ably  caused  by  the  breaking  of  one  or  more  braces,  and  at 
pounds  the  boiler  was  seen  to  explode  with  terrible  force.  The 
whole  of  the  enclosure  was  obscured  by  the  vast  masses  of 
steam  liberated  ;  the  air  was  dotted  with  the  flying  fragments, 
the  largest  of  which  —  the  steam-drum  —  rising  first  to  a  height 
variously  estimated  at  from  200  to  400  feet,  fell  at  a  distance 
of  about  450  feet  from  its  original  position.  The  sound  of  the 
explosion  resembled  the  report  of  a  heavy  cannon.  The  boiler 
was  torn  into  many  pieces,  and  comparatively  few  fell  back 
upon  their  original  position. 


FIG.  153.— CORROSION. 

Thus  corrosion  may  affect  a  single  spot  in  a  boiler,  in  which 
case  a  "  patch,"  if  properly  applied,  should  make  the  boiler 
nearly  as  strong  as  when  whole.  A  series  of  weak  spots  near 
each  other  may  so  weaken  a  boiler  as  to  produce  explosion,  as 
may  any  considerable  area  of  thin  plate,  although,  when  occur- 
ring in  the  stayed  surfaces  of  a  firebox,  the  metal  may  become 
astonishingly  thin.  A  sketch  of  spots  of  corrosion  is  shown  in 
Fig.  153,  which  represents  the  cause  of  an  actual  explosion. 
This  cause  of  explosion  may  be  either  internal  or  external, 
and  is  induced  internally  by  bad  feed-water,  and  externally  by 
dampness  or  by  water  leaking  from  the  boiler,  either  unseen  or 
neglected.  It  is  always  dangerous  to  have  any  portion  of  a 
boiler  concealed  from  frequent  observation. 

The  effect  of  covering  a  part  of  a  sheet  subject  to  corrosion 
by  solid  iron,  as  by  the  lap  of  a  seam,  is  shown  in  the  next  fig- 
ure, which  also  exhibits  a  common  method  of  corrosion  along  a 
seam.  The  same  effect  is  seen  still  more  plainly  in  the  sue- 


6o6 


THE  STEAM-BOILER, 


ceeding  figure,  in  which  the  pitting  which  so  often  attends  the 
use  of  the  surface-condenser  is  also  well  shown. 

289.  The  Methods  of  Decay  are  as  various  as  the  forms 
and  location  of  the  parts  subject  to  corrosion.  As  Colburn*  has 
said :  "  As  a  malady,  corrosion  corresponds,  in  its  comparative 
frequency  and  fatality,  to  that  great  destroyer  of  human  life, 
consumption  ;"  and  it  has  as  innumerable  phases  and  periods  of 
action.  The  two  most  common  methods  of  decay  are  the  gen- 
eral, and  here  and  there  localized,  corrosion  that  goes  on  in  all 
boilers,  and  in  fact  on  all  iron  exposed  to  air  and  carbonic  acid, 
in  presence  of  moisture ;  and  the  concentrated  and  localized  oxi- 


FIG.  154.— CORROSION  AT  A  SEAM. 


FIG.  155.—"  PITTING.' 


dation  that  is  often  seen  along  the  line  of  a  seam  at  the  edge  of 
the  lap,  where  the  continual  changing  of  form  of  the  boiler  is  as 
constantly  producing  an  alternate  flexing  and  reflex  motion  of 
the  sheet,  which  throws  off  the  oxide  as  fast  as  formed  along 
that  line,  and  exposes  fresh,  clean  metal  to  the  corroding  influ- 
ence. A  groove  or  furrow  is  thus  in  time  produced,  which 
may,  as  occurred  in  the  case  of  the  Westfield  (Fig.  149),  actually 
cut  through  the  sheet  before  explosion  takes  place. 

The  phenomenon  known  as  "  grooving"  or  "  furrowing"  is 
well  illustrated  by  the  case  just  mentioned,  in  which  this  action 
was  originally  started,  probably,  by  the  carelessness  of  the  work- 
man, who,  either  in  chipping  the  edge  of  the  lap  along  a  girth- 


*  Trans.  Brit.  Assoc.  1884. 


STEAM-BOILER  EXPLOSIONS. 


607 


seam,  or  in  calking  the  seam,  scored  the  under-sheet  along  the 
edge  of  the  lap  with  the  corner  of  his  chisel  or  with  the  calk- 
ing-tool.  This  is  a  very  common  cause  of  such  a  defect. 

The  boiler  was  broken  into  three  parts.  The  first,  and  by 
far  the  largest  part,  consisted  of  the  furnaces,  steam-chimney 
and  flues,  with  a  single  course  of  the  shell  ;  the  second  con- 
sisted of  two  courses  of  the  outside  of  the  shell  next  the  back- 
head,  together  with  that  head,  to  which  they  remained  attached  ; 
the  third  piece  consisted  of  a  single  complete  course  from  the 
middle  of  the  cylindrical  shell,  which  was  separated  at  one  of 
its  longitudinal  seams,  partially  straightened  out  and  flung 
against  the  bottom  and  side  of  the  boat.  This  last  piece  re- 
mained opposite  its  original  position  in  the  boiler  before  the 
explosion,  while  the*  first  and  second  pieces  went  in  opposite 
directions,  the  former  finally  lying  several  feet  nearer  the  en- 
gine than  when  in  situ,  and  against  the  timbers  of  the  "  gallows- 
frame/' while  the  latter  piece  was  thrown  fifty  feet  forward  into 
the  bow  of  the  boat,  where  it  fell,  torn  and  distorted.  The 
longitudinal  seam,  along  which  piece  number  three  separated, 
and  the  deep  score  or  "  channel "  cutting  nearly  through  in  many 
places,  and  presenting  every  evidence  of  being 
an  old  flaw,  were  plainly  seen.  The  mark 
made  by  a  chisel  in  chipping,  and  that  of  the 
calking-tool,  were  seen,  and  indicated  the 
probable  initiative  cause  of  the  flaw. 

The  Author  examined  this  piece  and 
found  an  old  crack  or  "channel"  cut  along 
the  edge  of  the  horizontal  lap  referred  to  as 
being  at  the  ends  of  the  sheet,  and  in  some 
places  so  nearly  through  that  it  was  difficult 
to  detect  the  mere  scale  of  good  iron  left, 
while  in  other  places  there  remained  a  six- 
teenth of  an  inch  of  sound  metal.  Fig.  156 
exhibits  a  section  of  the  crack. 

Were  this  the  weakest  place  in  the  boiler,  and  the  least  thick- 
ness here  one  sixteenth  of  an  inch,  the  tensile  strength  being 
equal  to  the  average  determined  by  the  tests  made  of  the  iron,  the 
pressure  required  to  rupture  such  a  boiler,  ten  feet  in  diameter, 


FIG.  156. 


608  THE   STEAM-BOILER. 

would  be  44079  X  TV  X  2  -f-  120  =  47  pounds  per  square  inch, 
nearly.  A  pressure  of  27  or  28  pounds  would  burst  it  open 
where  the  least  thickness  was  slightly  more  than  one  thirty- 
second  of  an  inch.  One  portion  may  be  supported,  to  some 
extent,  by  a  neighboring  stronger  part.  Along  this  longitudi- 
nal seam  the  limit  of  strength  would  seem  to  have  been  about 
30  pounds  per  square  inch,  which  is  about  the  pressure  at 
which  the  boiler  exploded,  this  seam  ripping  for  a  distance  of 
several  feet.  The  original  strength  of  the  boiler  was  equal  to 
about  1 20  pounds  along  the  horizontal  seams, — its  then  weak- 
est parts, — provided  that  the  iron  had,  when  new,  the  average 
strength  of  the  specimens  which  we  have  tested.  In  the  ver- 
tical seams  may  be  seen,  in  some  places,  similarly  weakened 
portions,  the  cracks  running  usually  from  rivet  to  rivet,  and 
here  and  there  exhibiting  marks  that  show  the  wedging  action 
of  the  "  drift-pin,"  and  many  places,  both  in  longitudinal  and 
girth-seams,  are  cut  by  the  chisel  and  marked  by  the  "  calking- 
tool." 

These  lines  of  "  furrowing"  are  sometimes  continuous,  and 
sometimes  interrupted  by  portions  of  good  iron.  They  are 
probably  in  most  cases  caused  by  changes  in  form  of  the  boiler 
with  variations  of  temperature  and  pressure,  some  line  of  local 
weakness  determining  the  line  along  which  the  plate  shall  bend, 
and  this  bending  taking  place  continually,  though  ever  so 
slightly,  along  the  same  line  precisely,  finally  produces  rupture. 
This  change  of  form  of  the  shell  of  a  boiler  may  be  due  to 
either  the  constantly  occurring  variation  of  pressures,  as  steam 
is  made  or  is  blown  off  during  working  hours  ;  or  it  maybe  pro- 
duced by  changes  of  temperature.  Large  and  thin  boilers  are 
especially  liable  to  this  form  of  injury.  Bad  methods  of  sup- 
port may  permit  or  may  cause  variations  of  form  and  this  defect, 
which  is  all  the  more  dangerous  that  it  'is  difficult  in  many  cases 
to  detect  it.  Water  trickling  from  leaks  sometimes  causes  a 
kind  of  grooving  along  its  path,  hardly  less  serious  in  its  nature 
and  extent. 

Sometimes  this  action  produces  a  narrow  crack,  and  at  other 
times,  as  above  stated,  as  the  rust  formed  is  thrown  or  scoured 
off  the  iron  at  the  bend,  leaving  a  comparatively  clean  surface, 


STEAM-BOILER   EXPLOSIONS.  609 

oxidation  is  probably  accelerated,  and  the  fault  takes  the  form 
of  a  groove  or  furrow.  If  unperceived,  this  goes  on  until  a  rup- 
ture or  an  explosion  occurs. 

Of  forty  explosions  of  locomotive  boilers  noted  in  British 
Board  of  Trade  reports,*  eighteen  gave  way  at  the  firebox  and 
twenty  at  the  barrel.  Of  these  twenty,  every  one  was  the  re- 
sult of  "  grooving"  or  cracks  along  the  lap  of  seams,  all  of 
which  were  lap-joints.  The  grooves  were  most  common  ;  they 
always  occurred  along  the  edge  of  the  inside  overlap,  just  where 
the  changes  of  form  with  varying  pressure  would  concentrate 
their  effects.  Such  results  are  sometimes  also  seen  at  butt- 
joints,  especially  where  a  strip  has  been  used  inside.  The  rack- 
ing action  of  the  engines  may  produce  precisely  the  same  effect. 
Wherever  change  of  form  is  felt,  grooving  or  furrowing  and 
cracking  may  be  expected  to  be  found  in  time.  Where  the 
boiler  is  already  heavily  strained  along  one  of  these  lines  of  re- 
duced thickness,  any  slight  added  stress,  as  a  jar,  or  the  action 
of  a  calking-tool,  as  when  leaks  in  boilers  under  pressure  are 
being  calked,  may  precipitate  an  explosion,  the  break  follow- 
ing the  groove  or  crack  just  as  a  stretched  drum-head  may  yield 
to  the  scratch  of  a  knife. 

290.  Differences  in  Temperature  between  parts  of  a 
boiler  more  or  less  closely  connected  in  the  structure  may  pro- 
duce serious  strains,  and  some  instances  of  explosion  have  been 
attributed  to  this  cause. 

Changes  of  temperature  occur  as  steam  is  raised  or  blown  off 
from  a  boiler,  and  its  temperature  becomes  at  one  time  that  due 
the  steam-pressure,  and  then  it  falls  to  that  of  the  atmosphere 
each  time  steam  is  blown  off.  It  will  change  its  form  more 
or  less,  and  will  usually  be  subjected  to  some  strain  by  this  pro- 
cess. Again,  while  actually  at  work,  the  steam-space  and  upper 
portion  of  the  water-space  are  at  the  temperature  of  steam  at 
the  working  pressure,  while  the  lower  part  is  continually  vary- 
ing in  temperature  from  that  of  the  feed-water  to  the  maximum 
which  it  attains  after  entrance.  This  difference  of  temperature 

*  "  Wear  and  Tear  of  Steam-boilers."    F.  A.  Paget,  Trans.  Soc.  of  Arts,  1865  ; 
London,  1865,  p.  8. 

39 


6lO  THE    STEAM-BOILER. 

between  the  upper  and  lower  parts  of  the  boiler,  as  well  as  be- 
tween other  portions,  causes  a  continual  tendency  to  distortion  ; 
and  if  this  distortion  be  resisted,  a  stress  is  thrown  upon  the 
parts  equal  to  that  which  would  be  required,  acting  externally, 
to  remove  the  distortion,  if  produced.  The  stress  is  also  equal 
to  the  mechanical  force  that  would  be  necessary  to  produce 
similar  distortion. 

Thus,  had  the  temperature  of  the  main  and  upper  part  of 
the  Westfield's  boiler  been,  after  the  entrance  of  the  feed- 
water,  273°,  or  that  due  to  about  twenty-seven  or  twenty-eight 
pounds  steam,  while  the  feed-water  had  a  temperature  of  73°, 
the  bottom  of  the  boiler  having  a  temperature,  in  consequence, 
200°  below  that  of  the  top,  the  difference  in  length  would  be 
about  one  eight-hundredth,  and,  if  confined  by  rigid  abutments, 
iron  so  situated  would  be  subject  to  a  stress  of  twelve  and  a 
half  tons  per  square  inch.  But  in  this  case  one  part  would 
yield  by  compression  and  the  other  by  extension,  and  if  they 
were  to  yield  equally  it  would  reduce  the  stress  to  six  and  a 
quarter  tons.  Actually,  in  this  case,  the  lower  fourth  and  upper 
three  fourths  would  be  more  likely  to  act  against  each  other, 
and  the  stress,  if  the  boiler  had  no  elasticity  of  form,  would  be 
about  nine  tons.  Any  elasticity  of  form — and  boilers  generally 
possess  considerable — would  still  further  reduce  the  strain,  and 
it  very  frequently  makes  it  insignificant. 

It  is  thought,  by  some  experienced  engineers  and  other 
authorities,  that  many  of  the  explosions  known  to  have  taken 
place,  after  inspection  and  test,  at  pressures  lower  than  those  of 
the  test,  are  caused  by  the  weakening  action  of  unequal  expan- 
sion, the  stresses  and  strains  produced  in  this  manner  being 
superadded  to  those  due  to  simple  pressure,  against  which  latter 
the  boiler  might  otherwise  have  been  safe.  Such  effects  may 
also  be  the  final  provocative  to  explosion  when  cold  feed-water 
is  pumped  into  a  boiler,  on  getting  up  steam,  or  possibly,  some- 
times, when  cooling  off.  It  has  even  been  asserted  that  an 
empty  boiler  has  been  ruptured  by  such  changes  of  form  conse- 
quent on  building  a  light  fire  of  shavings  in  a  flue  to  start  the 
scale.  The  Author  has  known  of  instances  in  which  the  girth- 
seams  of  large  marine  flue-boilers  were  ruptured  along  the  line 


STEAM-BOILER  EXPLOSIONS.  6 1 1 

of  rivet-holes  a  distance  of  several  feet  by  the  introduction  of  a 
large  volume  of  cold  feed-water,  when  steam  was  up,  but  the 
engine  at  rest. 

The  differences  of  temperature  on  the  two  sides  the  sheet 
may  be  important.  While  it  is  true  that  the  heat  supplied  by 
the  furnace-gases  is  absorbed  by  the  boiler  to  the  same  extent, 
practically,  without  much  regard  to  the  thickness  of  the  plates 
of  the  boiler,  it  is  a  well-known  fact  that  the  resistance  of  iron 
to  the  flow  of  heat  is  so  great  that  the  effect  of  heat  on  the 
metal  itself  is  seriously  modified  by  the  thickness  of  the  sheet. 
Heavy  plates  "  burn"  away,  projecting  rivet-heads  are  destroyed, 
and  the  laps  of  heavy  plates  are  especially  liable  to  be  thinned 
seriously  where  they  are  employed. 

A  variation  of  temperature  of  considerable  range,  and  often 
recurring,  frequently  causes  injury  by  hardening  the  metal  of 
the  boiler,  making  it  brittle  and  liable  to  crack  with  change  of 
form,  and  also  produces  the  very  change  of  form  causing  this 
cracking. 

The  experiments  of  Lt.-Col.  Clark,  R.A.,*  show  that  great 
distortion  may  be  thus  produced.  It  is  probably  thus  that  iron 
and  especially  steel  fireboxes  so  often  crack,  in  consequence  of  a 
continual  swelling  of  the  metal  under  varying  temperatures  and 
the  stresses  so  caused.  This  action,  combined  with  oxidation, 
external  and  internal,  sometimes  makes  the  sheets  and  oftener 
the  stays  of  a  boiler  remarkably  weak  and  brittle ;  they  some- 
times become  more  like  cast  than  wrought  iron.  The  thicker 
the  sheet,  the  more  readily  is  it  overheated  and  overstrained. 

The  extent  to  which  alteration  of  form  under  pressure  may 
go,  with  good  material,  before  actual  rupture,  is  illustrated  by 
the  following  :f  During  the  summer  of  1868,  a  cylindrical  boiler, 
made  of  £-inch  steel  plates,  built  at  the  Fort  Pitt  Iron  Works, 
Pittsburg,  was  tested  under  authority  of  the  government,  with 
a  view  to  determining  the  relative  advantages  of  steel  and  iron 
as  a  material  for  navy  boilers.  When  the  pressure  of  cold  water 
had  reached  780  pounds,  the  girth  of  the  boiler  was  found  to 

*  Proc.  Royal  Society,  1863;  Journal  Franklin  Institute,  1863. 
f  Iron  Age,  Sept.  26,  1872. 


6l2  THE    STEAM-BOILER. 

have  permanently  increased  3}  inches,  and  at  820  pounds  rup_ 
ture  occurred. 

Cases  have  been  known  in  which  a  steel  crown-sheet  has  be- 
come overheated,  and  has  sagged  down  until,  the  tube-sheet 
going  with  it,  a  basin-shaped  form  has  been  produced,  convex 
toward  the  fire,  and  yet  no  fracture  produced,  even  when  the 
pump  was  put  on  and  the  boiler  filled  up  again  under  pressure. 

291.  The  Management  of  the  Steam-boiler,  or,  more 
correctly,  its  mismanagement,  while  in  operation,  and  a  neglect 
of  proper  supervision  and  inspection,  may  be  considered,  on 
the  whole,  the  usual  reason  of  explosion,  as  the  deterioration 
of  the  boiler  is  the  immediate  cause;  and  this  deterioration  is 
almost  invariably  so  gradual  and  so  readily  detected  by  intel- 
ligent and  painstaking  examinations  that  there  is  rarely  any 
excuse  for  its  resulting  disastrously.  A  well-made  boiler  under 
good  management  and  proper  supervision  may  be  considered 
as  practically  free  from  danger. 

The  person  in  direct  charge  of  the  boiler  is  usually  a  pre- 
sumably experienced  and  trustworthy  man.  He  should  be 
thoroughly  familiar  with  his  business,  generally  intelligent,  of 
good  judgment,  ready  and  prompt  in  emergencies,  and  abso- 
lutely reliable  at  all  times.  His  first  duty  is  to  see  that  the 
boiler  is  full  to  the  water-line,  trusting  only  the  gauge-cocks  ; 
he  must  keep  constant  watch  of  the  furnaces,  flues,  and  other 
surfaces  subject  to  the  action  of  the  fire,  and  thus  be  certain 
that  no  injury  is  being  done  by  overheating  or  sediment ;  he 
must  keep  the  feed-apparatus  in  perfect  working  order,  keep  up 
the  supply  of  water  continuously  and  regularly,  and  see  that 
the  safety-valve  is  in  good  order  at  all  times.  Such  careful 
management,  conscientious  inspection  and  cleaning,  and  repair- 
ing at  proper  intervals  will  insure  safety. 

To  keep  the  safety-valve  in  good  working  order  and  to  make 
certain  that  it  is  operative,  provision  should  be  made  for 
opening  it  by  hand,  and  it  should  be  daily  raised,  before  getting 
up  steam,  to  the  full  height  of  its  maximum  lift. 

Explosions  of  Gas  sometimes  precipitate  steam-boiler  explo- 
sions. Should  the  gases  leaving  the  fuel  and  the  furnace  not 
be  completely  burned,  but  become  so  mingled  in  the  flues  as  to 


STEAM-BOILER  EXPLOSIONS.  613 

produce  an  explosive  mixture,  combustion  finally  occurring,  the 
shock  may  be  sufficient  to  cause  rupture  of  the  boiler,  and,  as 
has  actually  sometimes  happened,  its  explosion.  Sewer-gases 
have  been  known  to  find  their  way  into  an  empty  boiler 
through  an  open  blow-off  pipe,  and  have  been  exploded  by  the 
first  light  brought  to  the  man-hole,  and  with  serious  damage  to 
adjacent  property.  Mineral  oils  used  to  detach  scale  have 
caused  similar  dangerous  and  sometimes  fatal  explosions  by  the 
ignition  of  the  mixture  of  their  vapors  and  the  air  within  the 
boiler.  It  is  important  that  care  be  taken  in  using  lights  about 
boilers  in  such  cases  of  application  of  mineral  oils. 

Explosions  of  gas  within  a  boiler  at  work  cannot  occur ;  but 
the  suggestion  of  the  possibility  of  such  an  occurrence  is  often 
made.  No  decomposition  of  water  can  take  place  except  a 
portion  of  the  boiler  is  overheated  ;  this  happening,  all  the 
oxygen  produced  is  absorbed  by  the  iron,  and  no  recombination 
can  occur  later,  even  were  it  possible  for  ignition  to  take  place 
under  the  conditions  producing  decomposition. 

The  flooding  of  a  boiler  with  water  until  it  is  filled  to  the 
steam-pipe  or  safety-valve  may  cause  so  serious  a  retardation  of 
the  outflow  of  the  mingled  fluids  as  to  result  in  overpressure 
and  great  danger.  Mr.  W.  L.  Gold  *  gives  the  following 
instances,  and  the  experience  of  the  Author  justifies  fully  his 
statement.  The  steam-pipe  or  the  safety-valve  cannot  relieve 
a  full  boiler  rapidly  and  safely. 

First,  a  boiler  38  inches  in  diameter,  two  flues,  shell  \  inch 
Juniata  iron,  ruptured  in  the  sheet  a  crack  9  inches  long,  steam- 
gauge  indicating  60  pounds,  safety-valve  weighted  at  80  pounds 
pressure.  This  rupture  closed  instantly ;  and  if  he  had  not  seen 
it  made,  he  might  possibly  have  been  surprised  by  an  explosion, 
with  water  and  steam  in  their  normal  condition,  very  shortly 
after.  Second,  a  steam-drum  (spanning  a  battery  of  five 
boilers)  30  inches  in  diameter.  The  blank-head  forced  (bulged) 
out  \\  inches,  the  stay-rods  stretched,  and  the  corner  of  the 
head-flange  cracked  one  third  around.  Third,  a  vertical  boiler, 
built  especially  to  carry  high  pressure  (safe  running  pressure 

*  Am.  Manufacturer,  Feb.  1881. 


6 14  THE   STEAM-BOILER. 

150  pounds),  the  hand-hole  and  man-hole  joints  forced  out  past 
the  flanges,  the  steam-pipe  joints  and  union  forced  out,  the 
packing  in  the  engine-piston  destroyed,  and  the  engine  gener- 
ally racked,  so  as  to  be  almost  useless.  Steam-pressure  by 
gauge  from  40  to  60  pounds ;  safety-valve  weighted  at  90 
pounds. 

Mr.  Gold  suggests  that,  as  this  is  a  not  infrequent  occur- 
rence, many  explosions  may  be  simply  the  final  act  in  the 
drama  commenced  by  the  feed-pump. 

292.  Emergencies  must  be  met  with  a  clear  head  and 
ready  wit,  with  perfect  coolness,  and  usually  with  both  prompt- 
ness and  quickness  of  action.  Every  man  employed  about 
steam-boilers,  as  well  as  every  engineer  and  every  proprietor, 
should  have  carefully  thought  out  the  proper  course  to  take  in 
any  and  every  emergency  that  he  can  conceive  of  as  likely  or 
possible  to  arise,  and  should  have  constantly  in  mind  the  means 
available  for  meeting  it  successfully.  When  the  time  comes  to 
act,  it  is  not  always,  or  even  often,  possible  to  take  time  to  study 
out  the  best  thing  to  be  done  ;  action  must  be  taken,  on  the 
instant,  based  on  earlier  thought  or  on  either  the  intuition  or 
the  impulse  of  the  moment. 

"  Low-water"  presents  perhaps  the  most  common,  as  well 
as  one  of  the  most  serious,  of  such  emergencies.  The  instant 
it  is  detected,  the  effort  must  be  made  to  check  the  fall  to  a 
lower  level ;  the  fire  must  be  dampened,  preferably  by  throwing 
on  wet  ashes,  and  the  boiler  allowed  to  cool  down.  Care 
should  be  taken  that  the  safety-valve  is  not  raised  so  as  to  pro- 
duce a  priming  that  might  throw  water  over  the  overheated 
metal,  and  that  no  change  is  made  in  the  working  of  either  en- 
gine or  boiler  that  shall  produce*  foaming  or  an  increased  pres- 
sure. If,  on  examination,  it  is  found  that  the  water  has  not  fallen 
below  the  level  of  either  the  crown-sheet  or  any  other  extended 
area  of  heating-surface,  the  pump  may  be  put  on  with  perfect 
safety;  but  if  this  certainty  cannot  be  assured,  the  boiler  should 
be  cooled  down  completely,  and  carefully  inspected  and  tested, 
and  thoroughly  repaired  if  injured.  If  no  part  of  the  exposed 
metal  is  heated  to  the  red  heat  there  is  no  danger,  except  from 
a  rise  in  the  water-level  and  flooding  the  hot  iron.  If  any  por- 


STEAM-BOILER  EXPLOSIONS. 

tion  should  be  red-hot,  an  additional  danger  is  due  to  the 
steam-pressure,  which  should  be  reduced  by  continuing  the  en- 
gine in  steady  working  while  extinguishing  the  fire.  If  the 
safety-valve  be  touched  at  such  a  time,  it  should  be  handled 
very  cautiously,  allowing  the  steam  to  issue  very  steadily  and 
in  such  quantities  that  the  steam-gauge  hand  shows  no  fluctua- 
tion, while  slowly  falling.  The  damping  of  the  fire  with  wet 
ashes  will  reduce  the  temperature  and  pressure  very  promptly 
and  safely.  The  Author  has  experimentally  performed  this 
operation,  standing  by  a  large  outside-fired  tubular  boiler  while 
all  the  water  was  blown  out,  and  then  covering  the  fire.  The 
pyrometer  inserted  in  the  boiler  showed  no  elevation  of  tem- 
perature until  all  the  water  was  gone,  and  the  fire  was  then  so 
promptly  covered  that  the  rise  wras  but  a  few  degrees,  and  the 
boiler  was  .not  injured.  As  it  proved,  there  was  not  the  slight- 
est danger  in  that  case;  but  with  less  promptness  of  action 
some  danger  might  have  arisen  of  injury  to  the  boiler,  although 
probably  not  of  explosion. 

Overheated  plates,  produced  by  sediment,  or  over-driving, 
resulting  in  the  production  of  •'  pockets"  or  of  cracks,  are,  virtu- 
ally, cases  of  low-water,  and  the  action  taken  should  be  the  same. 
The  boiler  being  safely  cooled  down,  the  injured  plate  should 
be  replaced  by  a  sound  sheet,  all  sediment  or  scale  carefully  re- 
moved, and  a  recurrence  of  the  causes  of  the  accident  effectively 
provided  against. 

Cracks,  suddenly  appearing  in  sheets  exposed  to  the  fire,  or 
elsewhere,  sometimes  introduce  a  serious  danger.  The  steps  to 
be  taken  in  such  a  case  are  the  immediate  opening  of  the  safety- 
valve  and  reduction  of  steam-pressure  as  promptly  and  rapidly 
as  possible,  meantime  quenching  the  fire  and  then  cooling  off 
the  boiler  and  ascertaining  the  extent  of  the  injury,  and  repair- 
ing it.  In  such  a  case,  unless  the  crack  is  near  the  safety-valve 
itself,  no  fear  need  be  entertained  of  too  rapid  discharge  of  the 
steam. 

Blistered  sheets  should  be  treated  precisely  as  in  the  cases 
preceding.  It  is  not  always  possible  to  surmise  the  extent  of 
the  injury  or  the  danger  involved  until  steam  is  off  and  an  ex- 
amination can  be  made.  It  is  not,  however,  absolutely  neces- 


6l6  THE   STEAM-BOILER. 

sary  to  act  as  promptly  as  in  the  preceding  cases ;  and  where 
the  blister  is  not  large  and  is  not  extending,  it  is  sometimes 
perfectly  allowable  to  await  a  convenient  time  for  blowing  off 
steam  and  making  repairs. 

An  inoperative  safety-valve,  either  stuck  fast,  or  too  small  to 
discharge  all  the  steam  made,  or  to  keep  the  pressure  down  to 
a  safe  point,  produces  one  of  the  most  trying  of  all  known  emer- 
gencies. In  such  a  case  steam  should  be  worked  off  through 
the  engine,  if  possible,  and  discharged  through  any  valves 
available,  through  the  gauge-cocks,  or  even  through  a  few  scat- 
tered rivet-holes,  out  of  which  the  rivets  may  be  knocked  on 
the  instant ;  the  fire  being  meantime  checked  by  the  damper 
or  by  free  use  of  water.  The  throwing  of  water  into  a  furnace 
is  often  a  somewhat  hazardous  operation,  however,  and  if  neces- 
sary, should  be  performed  \vith  some  caution,  to  avoid  risk  of  in- 
jury of  either  the  person  attempting  it,  or  of  the  boiler.  The 
use  of  wet  ashes  is  preferable.  In  all  cases  in  which  it  is  to  be  at- 
tempted to  reduce  the  rate  of  generation  of  heat,  closing  the  ash- 
pit doors  as  well  as  opening  the  fire-doors  will  be  of  service  by 
checking  the  passage  of  hot  air  from  below  and  accelerating 
the  influx  of  cold  air  above  the  grate  ;  but  the  closing  of  the 
ash-pit  involves,  with  a  hot  fire,  some  risk  of  melting  down  the 
grates. 

293.  The  Results  of  Explosions  of  steam-boilers,  in 
spreading  destruction  and  death  in  all  directions,  are  so  famil- 
iar as  scarcely  to  require  illustration ;  but  a  few  instances  may 
be  described  as  examples  in  which  the  stored  energy  of  various 
types  of  boiler  has  been  set  free  with  tremendous  and  impres- 
sive effect. 

Referring  to  the  table  in  §  269,  and  to  case  No.  I  :  The  explo- 
sion of  a  boiler  of  this  form  and  of  the  proportions  here  given, 
in  the  year  1843,  m  the  establishment  of  Messrs.  R.  L.  Thurston 
&  Co.,  at  Providence,  R.  L,  is  well  remembered  by  the  Author. 
The  boiler-house  was  entirely  destroyed,  the  main  building 
seriously  damaged,  and  a  large  expense  was  incurred  in  the  pur- 
chase of  new  tools  to  replace  those  destroyed.  No  lives  were 
lost,  as  the  explosion  fortunately  occurred  after  the  workmen 
had  left  the  building.  A  similar  explosion  of  a  boiler  of  this 


STEAM-BOILER  EXPLOSIONS.  6l/ 

size  occurred  some  years  later,  within  sight  of  the  Author,  which 
drove  one  end  of  the  exploding  boiler  through  a  1 6-inch  wall, 
and  several  hundred  feet  through  the  air,  cutting  off  an  elm- 
tree  high  above  the  ground,  where  it  measured  9  inches  in  di- 
ameter, partly  destroying  a  house  in  its  further  flight,  and  fell 
in  the  street  beyond,  where  it  was  found  hot  and  dry  immedi- 
ately after  striking  the  earth.  Long  after  the  Author  reached 
the  spot,  although  a  heavy  rain  was  falling,  it  was  too  hot 
to  be  touched,  and  was  finally,  some  time  later,  cooled  off  by  a 
stream  of  water  from  a  hose,  in  order  that  it  might  be  moved 
and  inspected.  It  had  been  overheated,  in  consequence  of  low- 
water,  and  cold  feed-water  had  then  been  turned  into  it.  The 
boiler  was  in  good  order,  but  four  years  old,  and  was  considered 
safe  for  no  pounds.  The  attendant  was  seriously  injured,  and 
a  pedestrian  passing  at  the  instant  of  the  explosion  was  buried 
in  the  ruins  of  the  falling  walls  and  killed.  The  energy  of  this 
explosion  was  very  much  less  than  that  stored  in  the  boiler 
when  in  regular  work. 

A  boiler  of  class  No.  3,  which  the  Author  was  called  upon 
to  inspect  after  explosion,  had  formed  one  of  a  "  battery"  of 
ten  or  twelve,  and  was  set  next  the  outside  boiler  of  the  lot.  Its 
explosion  threw  the  latter  entirely  out  of  the  boiler-house  into 
an  adjoining  yard,  displaced  the  boiler  on  the  opposite  side, 
and  demolished  the  boiler-house  completely.  The  exploding 
boiler  was  torn  into  many  pieces.  The  shell  was  torn  into  a 
helical  ribbon,  which  was  unwound  from  end  t6  end.  The  fur- 
nace-end of  the  boiler  flew  across  the  space  in  front  of  its  house, 
tore  down  the  side  of  a  "  kier-house,"  and  demolished  the  kiers, 
nearly  killing  the  kier-house  attendant,  who  was  standing  be- 
tween two  kiers.  The  opposite  end  of  the  boiler  was  thrown 
through  the  air,  describing  a  trajectory  having  an  altitude  of 
fifty  feet  and  a  range  of  several  hundred,  doing  much  damage 
to  property  en  route,  finally  landing  in  a  neighboring  field.  The 
furnace  front  was  found  by  the  Author  on  the  top  of  a  hill,  a 
quarter  of  a  mile,  nearly,  from  the  boiler-house.  The  attendant, 
who  was  on  the  top  of  the  boiler  at  the  instant  of  the  explo- 
sion, opening  a  steam-connection  to  relieve  the  boiler,  then  con- 


6l8  THE   STEAM-BOILER. 

taining  an  excess  of  steam  and  a  deficiency  of  water,  was 
thrown  over  the  roof  of  the  mill,  and  his  body  was  picked  up 
in  the  field  on  the  other  side,  and  carried  away  in  a  packing- 
box  measuring  about  two  feet  on  each  side.  The  cause  was 
low-water  and  consequent  overheating,  and  the  introduction  of 
water  without  first  hauling  fires  and  cooling  down.  Both  this 
boiler  and  the  plain  cylinder  are  thus  seen  to  have  a  projectile 
effect  only  to  be  compared  to  that  of  ordnance. 

The  violence  of  the  explosion  of  the  locomotive  boiler  is 
naturally  most  terrible,  exceeding,  as  it  does,  that  of  ordnance 
fired  with  a  charge  of  150  pounds  of  powder  of  best  quality,  or 
perhaps  250  pounds  of  ordinary  quality  fired  in  the  usual  way.* 
On  the  occasion  of  such  an  explosion  which  the  Author  was 
called  upon  to  investigate,  in  the  course  of  his  professional  prac- 
tice, the  engine  was  hauling  a  train  of  coal  cars  weighing  about 
1000  tons.  The  steam  had  been  shut  off  from  the  cylinders  a 
few  minutes  before,  as  the  train  passed  over  the  crest  of  an  in- 
cline and  started  down  the  hill,  and  the  throttle  again  opened 
a  few  moments  before  the  accident.  The  explosion  killed  the 
engineer,  the  fireman,  and  a  brakeman,  tore  the  firebox  to 
pieces,  threw  the  engine  from  the  track,  turning  it  completely 
around,  broke  up  the  running  parts  of  the  machinery,  and  made 
very  complete  destruction  of  the  whole  engine.  There  was  no 
indication  that  the  Author  could  detect  of  low-water ;  and  he 
attributed  the  accident  to  weakening  of  the  fire  box  sheets  at 
the  lower  parts  of  the  water-legs  by  corrosion.  The  bodies  of 
the  engineer  and  fireman  were  found  several  hundred  feet  from 
the  wreck,  the  former  among  the  branches  of  a  tree  by  the  side 
of  the  track.  This  violence  of  projection  of  smaller  masses 
would  seem  to  indicate  the  concentration  of  the  energy  of  the 
heat  stored  in  the  boiler,  when  converted  into  mechanical  en- 
ergy, upon  the  front  of  the  boiler,  and  its  application  largely  to 
the  impulsion  of  adjacent  bodies.  The  range  of  projection  was, 


*  The  theoretical  effect  of  good  gunpowder  is  about  500  foot-tons  per  pound 
(340  tonne-metres  per  kilogramme),  according  to  Noble  and  Abel. 


S  TEA M-B OIL ER  EXPLOSIONS. 


619 


in  one  case,  fully  equal  to  the  calculated  range.     The  energy 
expended  is  here  nearly  the  full  amount  calculated. 

Figs.  157,  158,  159,  1 60  illus- 
trate the  explosion  of  two  large  boil- 
ers which  produced  very  disastrous 
effects,*  killing  the  attendant  and  de- 
stroying the  boiler-house  and  other 
property.  These  boilers  were  hori- 
zontal, internally-fired,  drop-flue  boil- 
ers, seven  feet  diameter  and  twenty- 
one  feet  long,  the  shells  single-riv- 
eted, originally  five  sixteenths  of  an 
inch  thick. 

The  two  exploded  boilers  were 
made  twenty-one  years  before  the 
explosion,  and  worked,  as  their  mak- 
ers intended,  at  about  thirty  pounds 
per  square  inch,  till  about  twenty 
months  before  the  explosion,  at  which 
time  additional  power  was  required, 
and  the  pressure  was  increased  to  and  limited  at  fifty  pounds. 

A  third  boiler  did  not  explode,  but  was  thrown  about  fifty 
feet  out  of  its  bed. 


FIG.  157.— EXPLOSION  OF  BOILERS  AT 
BROOKLYN,  N.  Y. 


FIG.  158. — POSITION  OF  THE  THREE  BOILERS  AFTER  THE  EXPLOSION. 

A  few  minutes  before  noon,  while  the  engine  was  running  at 
the  usual  speed,  the  steam-gauge  indicating  forty-seven  pounds 

*  Scientific  American,  May  20,  1882. 


62O 


THE   STEAM-BOILER. 


pressure,  and  the  water-gauges  showing  the  usual  amount  of 
water,  the  middle  one  exploded  :  the  shell  burst  opm,  and  was 
nearly  all  stripped  off.  The  remainder  of  the  boiler  was  thrown 
high  in  the  air. 

While  this  boiler  was  in  the  air,  No.  I,  the  left-hand  boiler, 
having  been  forcibly  struck  by  parts  of  No.  2,  also  gave  way  so 


FIG.  159. — INITIAL  RUPTURE. 

that  its  main  portion  was  projected  horizontally  to  the  front, 
arriving  at  the  front  wall  of  the  building  in  time  to  fall  under 
No.  2,  as  shov/n  in  Fig.  158.  The  most  probable  method  of  rup- 
ture is  indicated  in  Fig.  159,  as  the  line  AB  separates  a  ring  of 
plates  which  was  found  folded  together  beneath  the  pile  of  dt- 


FIG.  160,— INTERIOR  OF  BOILER-HOUSE  PRIOR  TO  THE  EXPLOSION. 

bris.  If  the  initial  break  had  been  at  some  point  on  the  bot- 
tom, this  belt  of  plates  would  have  been  thrown  upward  and 
flattened,  instead  of  downward,  where  it  was  thrown  by  the  flood 
of  water  from  No.  I  boiler. 

The  third  boiler  was  raised  from  its  bed  by  the  issuing  water, 
and  thrown  about  fifty  feet  to  the  right  of  its  original  position. 


STEAM-BOILER   EXPLOSIONS. 


621 


These  two  boilers  contained  probably  more  than  fourteen 
tons  of  water,  which  had   a  temperature  due  to  forty-seven 


FIG.  161. — EXPLODED  LOCOMOTIVE. 


pounds  of  steam,  and  the  effect  of  its  sudden  liberation  was 

equal  that  of  several  hundred  pounds  of  exploded  gunpowder. 

The  terrible  wreck  usually  consequent  upon  the  explosion 


FIG.  162.— TUBES  OF  AN  EXPLODED  BOILER. 


of  a  locomotive  boiler  is  well  illustrated  in  the  accompanying 
engraving,  which  represents  the  results  of  such  an  explosion  on 
the  Fitchburg  Railway,  August  13,  1877;  while  the  havoc 


622  THE   STEAM-BOILER. 

wrought  among  the  tubes  on  such  occasions  is  as  strikingly 
illustrated  in  Fig.  162. 

In  the  case  of  an  explosion  of  a  locomotive  investigated  by 
a  commission  of  which  the  Author  was  a  member,  the  train  was 
moving  slowly  when  the  boiler  exploded  with  a  loud  report ; 
the  locomotive  was  turned  completely  over  backward,  carrying 
with  it  and  burying  the  fireman  beneath  the  ruins. 

Nothing  could  at  first  be  found  of  the  engineer.  Parties 
searched  for  long  distances  about  the  wreck  for  signs  of  the  un- 
fortunate man,  but  it  was  not  until  next  morning  that  his  body 
was  found.  It  was  discovered  lying  in  the  woods,  seven  hun- 
dred feet  away  from  the  locomotive. 

The  locomotive  was  completely  demolished,  and  every  part 
of  the  machinery  was  twisted  or  broken  into  pieces.  The  track 
was  torn  up  for  some  distance,  and  rails  were  bent  like  coils  of 
rope.  The  firebox  of  the  locomotive  was  hurled  from  its  posi- 
tion and  broken  into  many  pieces.  A  large  piece  weighing 
many  hundred  pounds  was  carried  five  hundred  feet.  The 
dome  and  sand-box  were  thrown  an  eighth  of  a  mile  into  the 
adjacent  river.  The  wheels  ot  the  engine  were  torn  off,  and  no 
one  piece  of  the  cab  was  discovered.  The  engineer  bore  an 
excellent  reputation  as  being  a  careful  man,  always  carrying  a 
large  supply  of  water.  The  engine  was  one  of  approved  make, 
and  had  been  in  use  for  fifteen  years.  It  had  just  come  from  the 
repair-shop.  A  new  firebox  had  been  put  in  three  years  before, 
and  the  boiler  was  thoroughly  examined  about  six  weeks  earlier. 
The  iron  was  in  many  cases  twisted  and  bent  into  shapeless  rolls. 
The  point  of  rupture  was  apparently  in  the  left-hand  lower  cor- 
ner of  outside  shell  of  the  firebox.  The  cause  was  variously  as- 
signed as  a  percussion  or  "  fulminating"  action  due  to  overheated 
iron  and  to  certain  defective  portions  of  the  firebox.  The  latter 
was  probably  the  true  cause. 

The  following  may  be  taken  as  another  illustration  of  the 
tremendous  effects  of  explosion  at  usual  working  pressure,  with 
an  ample  supply  of  water :  A  boiler  of  the  locomotive  type  was 
constructed  for  use  in  a  small  steamer.  Its  shell  was  of  iron,  4 
feet  in  diameter,  and  T5¥ths  inch  thick.  It  was  " tested''  by 
filling  with  water  and  raising  steam.  It  exploded  with  the 


STEAM-BOILER  EXPLOSIONS.  623 

safety-valve  set  at  120  pounds  pressure  per  square  inch,  blow- 
ing freely,  although  held  down  by  the  man  in  charge,  and  killed 
and  injured  several  people.  The  hiss  of  steam  escaping  from  the 
initial  rupture  was  heard  an  instant  before  the  explosion.  The 
boiler  was  turned  end  for  end,  and  the  firebox  torn  from  the 
boiler  in  two  pieces,  one  being  carried  to  a  distance  of  about 
500  feet  and  imbedded  in  the  mud  of  a  canal-bed ;  the  other  por- 
tion, weighing  about  4800  pounds,  was  carried  a  distance  of  be- 
tween 400  and  500  feet,  and  crashed  into  the  side  of  a  building 
filled  with  sash,  blinds,  and  doors  piled  closely  together.  This 
piece  of  iron  comprised  the  firebox,  the  dome,  and  the  end  of 
the  boiler,  and  was  straightened  into  a  piece  30  feet  long  and 
four  feet  wide.  This  piece  is  said  to  have  rushed  through  the 
air  with  a  whirling  motion  until  it  struck  the  building.  It  cut 
the  side  of  the  building  and  beams  and  rafters  like  straws,  push- 
ing the  front  of  the  building  forward  several  feet.  Fragments 
of  the  boiler  were  found  at  many  points  considerably  distant 
from  the  scene  of  the  explosion,  and  in  many  places  windows 
were  shattered  by  the  concussion. 

The  shell  of  the  boiler  was  reversed  by  the  force  of  the 
explosion,  with  such  force  that  one  end  was  buried  four  feet  in 
the  road-bed.  All  the  flues  remained  in  the  boiler,  one  end  of 
which  was  torn  from  them  while  the  other  remained  in  place. 
At  the  instant  of  the  explosion  the  air  for  many  feet  in  every 
direction  was  filled  with  flying  fragments,  many  of  them  being 
thrown  to  a  great  height. 

In  one  case  coming  under  the  observation  of  the  Author,  a 
locomotive  set  as  a  stationary  boiler  gave  way  in  the  firebox, 
and  let  out  the  water  and  steam,  but  injured  no  one.  The  rent 
was  about  twelve  inches  long  and  eight  inches  wide.  The  iron 
in  that  place  was  weakened  by  corrosion,  otherwise  the  boiler 
was  in  good  condition.  Repairs  were  immediately  commenced 
and  the  boiler  was  ready  for  use  next  day.  Had  this  rent  oc- 
curred at  or  above  the  water-level,  it  is  very  possible  that  an 
explosion  may  have  resulted,  in  the  manner  suggested  by  Clark 
and  Colburn. 

In  an  explosion  of  a  tubular  boiler  at  Dayton,  O.,  Oct.  25, 


624 


THE    STEAM-BOILER. 


1 88 1,*  by  which  several  lives  and  much  property  were  destroyedr 

the  rupture  started  along  the  lap 
AB  in  the  figure,  and  was  evi- 
dently due  to  the  furrowing  which 
had  been  there,  in  some  way,  pro- 
duced. The  boiler  was  less  than 
a  year  old,  and  was  reported  to  be 
of  good  material  and  workman- 
ship. The  longitudinal  seams  were 
double-riveted,  and  it  is  very  pos- 
sible that  the  stiffness  thus  pro- 

FIG.  163. — INITIAL  RUPTURE;  "GROOVING."  .... 

duced  along  their  lines  may  have 

so  localized  the  strains  due  to  alterations  of  form  as  to  have  led 
to  this  fatal  result,  aided  by  the  action  of  the  calking-tool,  the 


FIG.  164. — BOILER-EXPLOSION  AT  DAYTON,  OHIO. 

marks  of  which  along   the  line  at  which  the  crack  gradually 

worked  through  the  sheet  were  plainly 
visible.  The  boiler  had,  when  first  set 
in  place,  been  tested  to  140  pounds ; 
the  explosion  occurred  at  probably  less 
than  80. 

A  strip  of  plates,  as  in  Fig.  165,  was 

FIG.  165.— GIRDLE  OF  PLATES  TORN  torn  from  the  boiler,  separating  it  into 

FROM  No.  2  BOILER.  .  n , 

two  parts,  as  seen  in  the  two  succeeding 
figures,  and   throwing  them  apart  with  all  the  force  due  to  a 

*  Scientific  American,  Dec.  17,  1881. 


STEAM-BOILER   EXPLOSIONS. 


625 


hundred  millions  of  foot-pounds  of  available  stored  heat-energy, 
and  entirely  destroying  the  house  in  which  they  were  set. 

In    a   case  of   explosion    at    Pittsburg,   Pa.,   in    December, 
1 88 1,  a  battery  of  flue-boilers  was  connected,  as  seen  in  Fig. 


FIG.  i66«. 

REAR  END  OF  BOILER 
AFTER  EXPLOSION. 


FIG.  1 663. 

REAR  END  OF  BOILER  BE- 
FORE EXPLOSION. 


FIG.  167.— FRONT  END  OF  BOILER 
AFTER  EXPLOSION. 


169,  by  steam-drums  above  the  nearer  two  and  mud-drums 
beneath  all  three.  The  steam-pressure  was  not  far  from  125 
pounds  per  square  inch  at  the  time  of  the  accident.  The  boilers 


5.— Principal  part  of  No.  5  boiler,  thrown  over  the  church  on  the  bluff.    6.— Principal  part  of  No.  6  boiler. 
FIG.  168. — EXPLOSION  OF  Two  STEAM-BOILERS  AT  PITTSBURG,  PA. 

were  fifteen  years  old,  but  had  been  tested  to  170  pounds  two 
years  earlier,  and  allowed  to  work  at  120  pounds,  although  they 
had  been  repeatedly  patched  and  repaired.*  The  rules  of  the 


*  Scientific  American,  Feb.  4,  1882. 


40 


626 


THE    STEAM-BOILER. 


insurance   companies  would    have   allowed    but   one   half   this 
pressure. 

The  strains  produced  by  the  changes  of  form  with  varying 
temperature  of  feed-water,  and  by  the  action  of  the  new  iron  of 
the  patches  on  the  older  and  corroded  parts  of  the  boiler, 
started  cracks  which  gradually  weakened  them,  and  finally  led 


FIG.  169. — UNDER  SIDES  OF  BOILERS. 


to  a  rupture  along  the  worst  line  of  injury,  ABy  in  the  preced- 
ing figure,  opening  the  course  of  plates  at  a,  and  tearing  it  out 
as  in  the  next  figure,  in  which  AB  is  the  line  of  initial  fracture. 


FIG.  170. — COURSE  OF  PLATES  DETACHED. 

The  destruction  of  this  (No.  6)  boiler  was  accompanied  by  the 
disruption  of  that  next  it  (No.  5),  which  was  also  in  about  as 
dangerous  condition.  The  available  energy  of  the  explosion 
was  about  250,000,000  foot-pounds,  and  the  damage  produced 
was  proportional  to  this  enormous  power.  One  boiler  (No.  5) 
was  thrown  across  the  road  and  over  a  church ;  the  other  (No. 
6)  was  thrown  to  one  side,  partially  destroying  neighboring 
buildings.  The  boiler-house  was  entirely  destroyed.  The  third 
boiler  remained  unexploded,  and  was  found  a  little  out  of  place 
and  nearly  full  of  water. 


STEAM-BOILER  EXPLOSIONS.  62? 

According  to  the  observer  furnishing  these  particulars,  the 
conclusions  are  inevitable: 

(1)  That  the  two  boilers  exploded  in  succession  so  quickly 
as  to  be  practically  simultaneous,  beginning  at  the  weak  line 
AB  of  No.  6  boiler. 

(2)  That  they  contained  an  ample  supply  of  water. 

(3)  That  the  pressure  was  too  great  for  boilers  of  their  size 
and  condition. 

(4)  That  the  use  of  cold  feed-water  hastened  the  deteriora- 


FIG. 171.— PIECE  OF  PATCH. 

tion  of  poor  iron,  causing  cracks  and  leaks,  by  which  external 
corrosion  was  produced,  and  that  the  energy  stored  in  the 
water  of  these  boilers  caused  all  the  destruction  observed. 

It  is  always  to  be  strongly  recommended  that  regular  and 
continuous  feeding  of  hot  water  be  practised ;  and  that  the 
greatest  care  be  exercised  by  inspectors  and  those  in  charge  of 
steam-boilers  in  searching  for  and  immediately  repairing  dan- 
gerous defects. 

The  last  figure  is  an  excellent  illustration  of  the  appearance 
of  iron  when  thus  corroded  and  cracked.  At  C  the  crack  was 
old,  and  partly  filled  up  with  lime-scale. 

The  explosion  of  the  upright  tubular  boiler  is  usually  con- 
sequent upon  some  injury  of  its  furnace,  either  by  collapse 
or  by  the  yielding  of  the  tube-sheet  to  excessive  pressure. 
The  result  is  commonly  the  projection  of  the  boiler  upward 
like  a  rocket,  and  is  rarely  accompanied  by  much  destruction 
of  property  laterally.  A  typical  case  of  this  kind  is  that  of  an 


628 


THE   STEAM-BOILER. 


explosion  occurring  at    Norwich,  Connecticut,  December   23, 
1 88 1,  of  which  the  following  is  a  brief  account :  * 


FIG.  172. — EXPLOSION  OF  AN  UPRIGHT  BOILER. 

Fig.  253  represents  the  location  of  the  boiler  and  engine 
immediately  before  the  explosion.     The  explosion  took  place, 

as  shown  in  figure,  by  the  yielding 
of  the  lower  tube-plate  of  the  boiler. 
This  boiler  was  three  feet  in  diam- 
eter and  seven  feet  high,  and  was 
four  years  old.  The  boiler  was 
made  of  five-sixteenths  iron  through- 

o 

out.  It  contained  sixty  tubes,  two 
inches  in  diameter,  five  feet  long, 
which  were  set  with  a  Prosser  ex- 
pander, and  were  beaded  over  as 
usual.  The  upper  tube-head  was 
flush  with  the  top  of  the  shell,  and 
the  lower,  forming  the  crown  of  the 
furnace,  was  about  two  feet  above 
the  grates  and  the  base  of  the  shell, 
and  was  flanged  upon  the  inner  sur- 
face of  the  furnace.  There  was  a 
safety-plug  in  the  lower  tube-head, 
which  was  not  melted  out,  although,  as  is  often  the  case  when 

*  Scientific  American,  Jan.  14,  1882. 


FIG.  173. — BOILER-ROOM  BEFORE  THE 
EXPLOSION. 


S TEA M- BOILER  EXPL 0 SIGNS. 


629 


these  plugs  are  so  near  the  fire,  a  portion  of  the  lower  part  of 
the  fusible  filling  had  disappeared. 

The  working  pressure  was  sixty  pounds  per  square  inch, 
and  the  explosion  probably  took  place  at  or  a  little  below  this 
pressure,  throwing  the  boiler  through  the 
roof  and  high  over  a  group  of  buildings, 
and  a  tall  tree  close  by,  finally  burying 
itself  half  its  diameter  in  the  frozen  ground. 
There  had  been  leak  in  the  tubes,  and 
four  had  been  plugged.  There  was  a 
crack  in  the  upper  head  near  the  centre, 
which  extended  between  three  tubes. 
From  this  crack  steam  escaped,  and  the  water  had  settled  upon 
the  surrounding  surface  of  the  tube-head  and  the  tube-ends. 
The  result  was  to  reduce  the  five-sixteenths  plate  to  less  than  a 
quarter  of  an  inch  in  thickness,  and  the  tube-ends  to  the  thick- 
ness of  writing-paper.  The  lower  tube-ends  had  suffered  still 


FIG.  174. — YIELDING  TUBE- 
SHEET. 


FIG.    175. — THE  EXPLODED  BOILER. 

more  from  leaks,  and  were  as  thin  as  paper,  and  afforded  no 
adequate  support  to  the  head.  The  pressure  consequently 
forced  the  lower  head  down,  opening  fifty  or  more  holes  two 
inches  diameter,  from  which  the  fluid  contents  of  the  boiler 
issued  at  a  high  velocity  and  the  whole  boiler  became  a  great 
rocket,  weighing  about  two  thousand  pounds. 


630 


THE   STEAM-BOILER. 


One  life  was  destroyed  by  this  explosion  and  a  considerable 
amount  of  property. 

An  explosion  which  occurred  at   Jersey  City,  N.  J.,  some 
years  ago,  illustrates  at  once  the  dangers  of  low-water  and  of 

a  safety-valve  rusted  fast.  As  re- 
ported at  the  time,*  "  The  boiler 
wras  of  the  locomotive  type,  having 
a  dome  upon  the  top.  The  en- 
gineer upon  the  morning  of  the  ex- 
plosion lighted  the  fire  in  the  boiler, 
and  shortly  afterwards  was  called 
away,  leaving  the  boiler  in  charge 
of  his  nephew,  who  was  young  and 
inexperienced  in  the  handling  of 
steam.  After  putting  fresh  coal  in 
the  furnace  he  was  called  away  by 
one  of  the  owners  of  the  dock  to 
assist  at  some  outside  duty.  Upon 
his  return  he  saw  the  seams  of  the 
boiler  opening,  and  attempted  to 
open  the  furnace-door,  but  was  un- 
able, owing  to  the  excess  of  pressure  of  steam  within  the  boiler 
which  had  caused  the  head  to  change  its  shape.  A  few  mo- 
ments afterwards  the  explosion  occurred,  the  firebox  being 
thrown  downwards,  the  top  of  the  shell  and  crown-sheet  up- 
wards, while  the  cylinder  part  shot  directly  up  the  street.  It 
struck  the  ground  about  400  feet  from  its  original  position,, 
demolished  a  fire-hydrant,  several  trucks,  trees,  and  a  horse,  and, 
spinning  end  for  end,  came  to  rest  by  the  side  of  a  truck,  which 
it  destroyed,  about  642  feet  from  its  starting-point.  Subse- 
quent investigation  revealed  the  fact  that  the  boiler  was  not 
properly  supplied  with  water.  A  portion  of  the  crown-sheet 
which  we  examined  showed  conclusively  that  near  the  flues  it 
was  red-hot.  We  also  examined  the  safety-valve,  which  was  of 
the  wing  pattern,  having  a  lever  and  weight.  This  valve  was 
so  firmly  corroded  to  its  seat  that  it  could  not  be  removed,  and 


FIG.  176. — THE  EXPLOSION. 


Am.  Machinist,  Oct.  i,  1881. 


STEAM-BOILER  EXPLOSIONS. 


63I 


the  stem  was  also  corroded  fast.  The  whole  secret  of  this  ex- 
plosion is  that  the  boiler  was  short  of  water,  and  an  excessively 
high  pressure  of  steam  was  raised  to  an  unknown. point,  which, 
without  relief,  acquiring  sufficient  force,  tore  the  boiler  to 
pieces." 

The  valve  was  found,  and,  being  placed  in  a  testing-ma- 
chine then  under  the  charge  of  the  Author,  at  the  Stevens  In- 
stitute of  Technology,  was  only  started  by  a  pressure  of  a  ton 
and  a  half,  *  while  nearly  two  tons  was  required  to  move  it 
observably, 

Change  of  form  with  varying  pressures  and  temperatures 
sometimes  produces  most  unexpected  defects.  It  has  been  ob- 
served that  many  locomotive  boilers 
stayed  as  in  the  figuref  give  way  at 
the  side,  in  the  manner  here  exhib- 
ited. Investigation  shows  that  in 
these  cases  the  tying  of  the  furnace- 
crowns  to  the  shell  by  the  system  of 
staying  illustrated,  and  the  continual 
rising  and  falling  of  the  furnace  rel- 
atively to  the  shell,  is  very  apt  to 
cause  a  buckling  of  the  outside  sheet 
along  the  horizontal  seam,  which 
finally  yields.  This  buckling  and 
straightening  of  the  sheet  goes  on  FlG- 177-— FAULTY  STAYING. 
until  a  crack  or  a  furrow  is  formed  along  the  lap  nearest  the  most 
rigid  brace,  and,  when  this  has  cut  deeply  enough,  the  side  of 
the  boiler  opens,  often,  the  whole  length  of  the  furnace,  the  ex- 
plosion doing  an  amount  of  damage  which  is  determined  by  the 
steam-pressure,  the  quantity  of  energy  stored,  and  the  extent 
of  the  rupture. 

In  these  cases,  either  the  crown-bars  over  the  furnace  or  the 
stays  should  alone  have  been  used ;  their  use  together  is 
objectionable.  Of  the  two  systems,  probably  the  first  is  the 
safer  in  such  boilers. 


*  Am.  Machinist,  Oct.  22,  1881. 
f  Locomotive,  Jan.  i,  1880. 


632  THE   STEAM-BOILER. 

The  appearance  of  a  collapsed  flue  is  seen  in  the  two  succeed- 
ing figures,  which  represent  the  results  of  experiments  made  by 
the  U.  S.  Commission  appointed  to  investigate  the  causes  of 


FIG.  178.— COLLAPSED  FLUES.  FIG.  179. — COLLAPSED  FLUES. 

explosions  of  steam-boilers.  In  neither  case  did  the  boiler 
move  far  from  its  original  position.  Collapsed  flues  rarely 
cause  extensive  destruction  of  property. 

The  explosion  of  a  rotary  rag-boiler,  receiving  steam  from 


FIG.  180.— AN  EXPLODED  BOILER. 

steam-boilers  at  a  distance,  which  took  place  at  Paterson,  N.  J., 
wrecked  the  mill,  destroyed  a  part  of  an  adjacent  establish- 
ment, and  caused  serious  loss  of  life  and  property.  The  dis- 
aster was  due  to  weakening  of  the  boiler  by  corrosion,  but,  not- 
withstanding its  reduced  strength,  the  shock  of  the  explosion 
was  felt  and  was  heard  throughout  the  city,  and  heavy  plate- 
glass  windows  were  broken  at  a  considerable  distance  from  the 
scene  of  the  accident.  Explosions  of  this  kind  show  the  fallacy 


STEAM-BOILER  EXPLOSIONS.  633 

of  many  of  the  absurd  and  mischievous  "  theories"  which  have 
been  prevalent  in  regard  to  explosions. 

Where  the  iron  or  steel  used  in  the  construction  of  the  boiler 
is  of  good  quality,  strong,  uniform,  and  ductile,  the  smaller  torn 
parts  of  an  exploded  boiler  may  not  break  away  from  the  main 
body;  such  a  case  is  illustrated  in  the  last  figure  (180),  which 
represents  the  effect  of  an  explosion  of  a  new  boiler  from 
a  cause  not  ascertained.  The  boiler  was  15  feet  long  by  4  feet 
diameter,  with  38  four-inch  flues.  Both  heads  remained  on  the 
flues,  but  the  shell  of  the  boiler  burst  along  the  rivet-holes 
nearly  all  around  both  heads,  as  shown  in  the  engraving. 

294.  Experimental  Investigations  of  the  causes  and 
methods  of  steam-boiler  explosions  have  been  occasionally 
attempted.  One  of  the  earliest  and  most  systematic,  as  well  as 
fruitful,  was  that  of  a  committee  of  the  Franklin  Institute, 
the  results  of  which  were  reported  to  the  Secretary  of  the  U.  S. 
Treasury  early  in  1836. 

This  committee  proposed  by  experiment — 

I.  To  ascertain  whether,  on  relieving  water  heated  to,  or 
above,  the  boiling-point,  from  pressure,  any  commotion  is  pro- 
duced in  the  fluid. 

To  determine  the  value  of  glass-gauges  and  gauge-cocks. 

The  investigation  of  the  question  whether  the  elasticity  of 
steam  within  a  boiler  may  be  increased  by  the  projection  of 
foam  upon  the  heated  sides,  more  than  it  is  diminished  by  the 
opening  made. 

II.  To   repeat  the  experiments  of  Klaproth    on    the   con- 
version of  water  into  steam  by  highly  heated  metal,  and  to 
make  others,  calculated  to  show  whether,  under  any  circum- 
stances, intensely  heated    metal  can   produce,  suddenly,  great 
quantities  of  highly  elastic  steam. 

To  directly  experiment  in  relation  to  the  production  of 
highly  elastic  steam  in  a  boiler  heated  to  high  temperature. 

III.  To  ascertain  whether  intensely  heated  and  unsaturated 
steam  can,  by  the  projection  of  water  into  it,  produce  highly 
elastic  vapor. 

IV.  When  steam  surcharged  with   heat    is   produced  in  a 


634  THE    STEAM-BOILER. 

boiler,  and  is  in  contact  with  water,  does  it  remain  surcharged, 
or  change  its  density  and  temperature  ? 

V.  To  test,  by  experiment,  the  efficacy  of  plates,  etc.,  of 
fusible  metal,  as  a  means  of  preventing  the  undue  heating  of  a 
boiler  or  its  contents. 

(1)  Ordinary  fusible  plates  and  plugs. 

(2)  Fusible  metal,  inclosed  in  tubes. 

(3)  Tables  of  the  fusing-points  of  certain  alloys. 

VI.  To  repeat  the  experiments  of  Klaproth,  etc. 

(1)  Temperature  of  maximum  vaporization   of  copper  and 
iron  under  different  circumstances. 

(2)  The  extension  to  practice,  by  the  introduction  of  differ- 
ent quantities  of  water,  under  different   circumstances  of  the 
metals. 

VII.  To  determine  by  actual  experiment  whether  any  per- 
manently elastic  fluids  are  produced  within  a  boiler  when  the 
metal  becomes  intensely  heated. 

VIII.  To  observe  accurately  the  sort  of  bursting  produced 
by  a  gradual  increase  of  pressure,  within  cylinders  of  iron  and 
copper. 

IX.  To  repeat  Perkins'  experiment,  and  ascertain  whether 
the  repulsion  stated  by  him  to  exist  between  the  particles  of 
intensely  heated  iron  and  steam  be  general,  and  to  measure,  if 
possible,  the  extent  of  this  repulsion,  with  a  view  to  determine 
the  influence  it  may  have  on  safety-valves. 

X.  To  ascertain  whether  cases  may  really  occur  when  the 
safety-valve,  loaded  with  a  certain  weight,  remains  stationary, 
while  the  confined  steam  acquires  a  higher  elastic  force  than 
that  which  would,  from  calculation,  appear  necessary  to  over- 
come the  weight  of  the  valve. 

XI.  To  ascertain  by  experiment  the  effects  of  deposits  in 
boilers. 

XII.  Investigation  of  the  relation  of  temperature  and  pres- 
sure of  steam  at  ordinary  working  pressures. 

It  is  only  necessary  here  to  state  that  the  results  proved — 
(i)  That  relieving    pressure   even  slightly  produced   great 
commotion  in  the  water,  and  considerably  relieving  it  caused 


STEAM-BOILER  EXPLOSIONS.  635 

the  violent  ejection  of  water  as  well  as  steam  through  the  open- 
ing by  which  the  pressure  was  reduced. 

(2)  That  under  similar  conditions  pressure  invariably  dimin- 
ished. 

(3)  That,  the  injection  of  water  upon  the  heated  surfaces  of 
the  experimental  boiler  produced  a  sudden  and  considerable 
rise  of  pressure. 

(4)  That  the  injection  of  water  into  superheated  steam  re- 
duced its  pressure  in  all  cases  noted. 

(5)  That  superheated  steam    may  remain   in  contact  with 
water  a  long  time  (two  hours  in  the  experiments  tried)  without 
becoming  saturated. 

(6)  That  fusible  plugs,  as  then  constructed,  were  unreliable, 
and  the  fusing-points  of  various  alloys  were  determined. 

(7)  That  the  temperature  of  maximum  vaporization  of  water 
is  lowered  by  smoothness  of  surfaces ;  that  of  iron  is  thirty  or 
forty  degrees  higher  than  that  of  copper,  while  the  time  required 
is  one  half  as  great  with  copper ;  that  the  temperature  of  maxi- 
mum vaporization,  for  oxidized  iron,  or   for   highly  oxidized 
copper,  is  about  350°  F.,  and  that  the  repulsion  between  the 
metal  and  the  water  is  perfect  at  from  twenty  to  forty  degrees 
above  the  temperature  of  maximum  vaporization. 

(8)  That  no  hydrogen  was  liberated  by  throwing  water  or 
steam  upon  heated  surfaces  of  the  boiler;  that  the  water  was 
not  decomposed,  and  that  air  cannot  occur  in  any  appreciable 
quantity  in  a  steam-boiler  at  work. 

(9)  That  "  all  the  circumstances  attending  the  most  violent 
explosions  may  occur  without  a  sudden  increase  of  pressure  with- 
in a  boiler"  the  explosion  being  produced  by  gradually  accu- 
mulated pressure. 

(10)  That  but  a  small  part  of  water,  highly  heated,  can  ex- 
pand into  steam,  if  suddenly  relieved  of  pressure. 

(11)  That  water  can  be  heated  to  very  high   temperature 
only  under  intensely  high  pressure. 

(12)  That  steam-pressure  may  rise  even  after  it  has  raised 
the  safety-valve. 

Unpublished  experiments  recently  made  by  Professor  Mason 
at  the  Rensselaer  Polytechnic  Institute  strongly  confirm  the  so- 


636 


THE   STEAM-BOILER. 


called  "  geyser  theory"  of  Messrs.  Clark  and  Colburn.  In  these 
experiments  a  number  of  miniature  boilers  were  constructed, 
and  were  exploded  by  a  gradually  produced  excess  of  pressure, 
and  in  such  manner  as  to  test  this  theory.  The  first  of  these 
boilers,  when  exploded,  produced  such  an  effect,  blowing  out 
windows  and  shaking  down  the  ceiling  of  the  laboratory  as 
effectually  to  dispose  of  the  idea  prevalent  among  certain  classes 
of  engineers  that  a  true  explosion  could  only  be  caused  by  low- 
water  and  overheated  plates.  Another  boiler  was  so  set  that,  the 
rear  end  being  lower  than  the  front,  the  quantity  of  water  acting 
by  percussion,  according  to  the  Clark  theory,  was  much  greater  at 
the  one  end  than  at  the  other.  The  consequence  was  that 
while  the  one  end  was  broken  into  many  pieces,  that  in  which 
there  was  least  water  was  simply  torn  from  the  mass  of  the 
boiler  and  was  itself  unbroken.  In  one  of  this  series  of  experi- 
ments the  boiler  was  broken  into  more  than  a  hundred  pieces, 
although  made  of  drawn  brass — a  material  far  less  liable,  ordi- 
narily, to  be  thus  shattered  than  iron  or  steel.  The  second  of 
the  above-described  experiments  appears  to  the  Author  a  very 
nearly  crucial  test  and  proof  of  the  theory  of  Messrs.  Clark  and 
Colburn. 


FIG.  181. — BOMB-PROOF. 

In  the  work  of  investigation  involving  the  explosion  of 
steam-boilers  it  is  usually  necessary  to  provide  a  safe  retreat  for 
the  observers,  from  which  to  watch  the  progress  of  the  experi- 
ment, and  from  which  to  read  the  steam-gauge,  to  watch  the 
water-level,  and  to  take  the  readings  of  the  thermometers  or 
pyrometers. 


STEAM-BOILER  EXPLOSIONS.  637 

The  illustration  represents  the  structure,  composed  of  heavy 
timber,  and  partially  underground,  used  at  the  testing-ground 
at  Sandy  Hook,  by  the  U.  S.  Commission  of  1873-6. 

These  experiments  were  projected  and  conducted  by  Mr. 
Francis  B.  Stevens  of  Hoboken,  and  at  the  request  of  Mr.  S. 
the  United  Railroad  Companies  of  New  Jersey  appropriated 
the  sum  of  ten  thousand  dollars  to  enable  Mr.  Stevens  to  enter 
upon  a  preliminary  series  of  experiments.  They  at  the  same 
time  invited  other  railroads  and  owners  of  steam-boilers  to  co- 
operate with  them,  and  offered  the  use  of  their  shops  for  any 
work  that  might  be  considered  necessary  or  desirable  during 
the  progress  of  the  work ;  no  such  aid  was,  however,  received. 

Several  old  boilers  had  recently  been  taken  out  of  the 
steamers  of  the  United  Companies.  These  were  subjected  to 
hydrostatic  pressure  until  rupture  occurred,  were  repaired  and 
again  ruptured  several  times  each,  thus  detecting  and  strength- 
ening their  weakest  spots,  and  finally  leaving  them  much 
stronger  than  when  taken  from  the  boats.  The  points  at  which 
fracture  occurred  and  the  character  of  the  break  were  noted 
carefully  at  each  trial. 

After  the  weak  spots  had  thus  been  felt  out  and  strength- 
ened, the  boilers  were  taken,  with  the  permission  of  the  War 
Department,  to  the  United  States  reservation  at  Sandy  Hook, 
at  the  entrance  to  New  York  harbor,  and  were  there  set  up  in 
a  large  inclosure  which  had  been  prepared  to  receive  them,  and 
the  four  old  steamboat-boilers  above  referred  to,  together  with 
five  new  boilers  built  for  the  occasion,  were  placed  in  their 
respective  positions  without  having  been  in  any  way  injured. 

Finally,  on  the  22d  and  23d  of  November,  the  experiments 
to  be  described  were  made. 

The  first  boiler  attacked  was  an  ordinary  "  single  return-flue 
boiler." 

The  cylindrical  portion  of  the  shell  wras  6  feet  6  inches 
diameter,  20  feet  4  inches  long,  and  of  iron  a  full  quarter  inch 
thick.  The  total  length  of  the  boiler  was  28  feet :  the  steam 
chimney  was  4  feet  diameter,  loj  feet  high,  and  its  flue  was  32 
inches  diameter.  The  two  furnaces  were  7  feet  long,  with  flat 
arches.  There  were  ten  lower  flues,  two  of  16  and  eight  of  9 


638 


THE   STEAM-BOILER. 


inches  diameter,  and  all  were  1 5  feet  9  inches  long ;  there  were 
twelve  upper  flues,  8J  inches  in  diameter,  and  22  feet  long. 
The  total  grate-surface  was  38^  square  feet,  heating-surface 
1350  square  feet.  The  water-spaces  were  4  inches  wide,  and 


FIG.  182. — MARINE  BOILER. 

the  flat  surfaces  were  stayed  by  screw  stay-bolts  at  intervals  of 
7  inches.  The  boiler  was  thirteen  years  old,  and  had  been 
allowed  40  pounds  pressure. 

The  upper  portion  of  the  boiler,  when  inspected  before  the 
experiment,  seemed  to  be  in  good  order.  The  girth-seams 
on  the  under  side  of  the  cylindrical  portion  had  given  way,  and 
had  all  been  patched  before  it  was  taken  out  of  the  boat.  The 
water-legs  had  been  considerably  corroded. 

In  September  this  boiler  had  been  subjected  to  hydrostatic 
pressure,  giving  way  by  the  pulling  through  of  stay-bolts  at  66 
pounds  per  square  inch.  It  was  repaired,  and  afterward,  at 
Sandy  Hook,  was  tested  without  fracture  to  82  pounds,  and 
still  later  bore  a  steam-pressure  of  60  pounds  per  square  inch. 

On  its  final  trial,  November  22d,  a  heavy  wood  fire  was  built 
in  the  furnaces,  the  water  standing  12  inches  deep  over  the 
flues,  and,  when  steam  began  to  rise  above  50  pounds,  the 
whole  party  retired  to  the  gauges,  which  were  placed  about 


STEAM-BOILER   EXPLOSIONS. 


639 


250  feet  from  the  inclosure.     The  notes  of  pressures  and  times 
were  taken  as  follows : 


TIME. 


PRESSURE.  TIME. 


PRESSURE.  TIME. 


PRESSURE.  TIME. 


PRESSURE. 


2.OO  P.M. 

58  Ibs. 

2.15  P.M. 

87  Ibs. 

2.25  P.M. 

91!  Ibs. 

2.40  P.M. 

91*  Ibs. 

2.05       " 

68    " 

2.20       " 

91*  " 

2.30       " 

91      " 

2-45       " 

91     " 

2.IO      ' 

78    " 

2.23       " 

93          i  2.35 

gii    ' 

2.50 

90 

The  pressure  rose  rapidly  until  it  reached  about  90  pounds,* 
when  leaks  began  to  appear  in  all  parts  of  the  boiler ;  and  at  93 
pounds  a  rent  at  (A,  Fig.  182)  the  lower  part  of  the  steam- 
chimney  where  it  joins  the  shell  becoming  quite  considerable, 
and  other  leaks  of  less  extent  enlarging,  the  steam  passed  off 


* 


FIG.  183. — STAYED  WATER-SPACE. 

more  rapidly  than  it  was  formed.  The  pressure  then  slowly 
diminishing,  the  workmen  extinguished  the  fires  by  throwing 
earth  upon  them,  and  the  experiment  thus  ended. 

The  second  experiment  was  made  with  a  small  boiler  (Fig. 
183),  which  had  been  constructed  to  determine  the  probable 
strength  of  the  stayed  surface  of  a  marine  boiler.  It  had  the 
form  of  a  square  box,  6  feet  long,  4  feet  high,  and  4  inches  thick. 
Its  sides  were  y5^  inch  thick,  of  the  "  best  flange  firebox"  iron. 
The  water-space  was  3f  inches  wide.  The  rivets  along  the 
edges  were  f  inch  diameter,  spaced  2  inches  apart.  The  two 


*  The  ultimate  strength  of  this  boiler,  when  new,  was  probably  equal  to  about 
double  this  pressure. 


640 


THE    STEAM  BOILER. 


sides  were  held  together  by  screw  stay-bolts,  spaced  8f  and 
inches,  and  their  ends  were  slightly  riveted  over,  precisely  copy- 
ing the  distribution  and  workmanship  of  a  water-leg  of  an  ordi- 
nary marine  boiler.  It  had  been  tested  to  138  pounds  pressure.. 
This  slab  was  set  in  "brickwork,  about  five  sixths  of  its  capacity 
occupied  by  water,  and  fires  built  on  both  sides.  Pressure 
rose  as  shown  by  the  following  extract  from  the  note-book  of 
the  Author : 


TIME.              PRESSURE. 

TIME.              PRESSURE. 

TIME.             PRESSURE.  TIME. 

PRESS  UR  i 

3.  18  P.M.         O  Ibs. 

3.28  P.M.        20  Ibs. 

3.37  P.M.      54  Ibs. 

3.46  P.M.      117  Ibs 

3.20 

4 

3.29 

23 

3.38 

58 

3-47 

126     ' 

3.21 

5 

3.30 

27 

3  39 

65 

3.48 

135   ' 

3.22 

7 

3-31 

30 

3-40 

72 

3-49 

147   ' 

3-23 

9 

3-32 

34 

3-41 

78 

3-50 

1  60  ' 

3-24 

3-25 

ii 

13 

3  33 
3-34 

38 
44 

3-42 
3-43 

86 
94 

3-51              165     ' 
Exploded. 

3.26 

15 

3-35 

49 

3-44 

100 

3-27 

18 

3.36 

51 

3-45 

no 

At  a  pressure  of  slightly  above  165,  and  probably  at  about 
167  pounds,  a  violent  explosion  took  place.  The  brickwork  of 
the  furnace  was  thrown  in  every  direction,  a  portion  of  it  rising 
high  in  the  air  and  falling  among  the  spectators  near  the  gauges  • 
the  sides  of  the  exploded  vessel  were  thrown  in  opposite  direc- 
tions with  immense  force,  one  of  them  tearing  down  the  high 
fence  at  one  side  of  the  inclosure,  and  falling  at  a  considerable 
distance  away  in  the  adjacent  field  ;  the  other  part  struck  one 
of  the  large  boilers  near  it,  cutting  a  large  hole,  and  thence 
glanced  off,  falling  a  short  distance  beyond. 

Both  sides  were  stretched  very  considerably,  assuming  a 
dished  form  of  8  or  9  inches  depth,  and  all  of  the  stay-bolts  drew 
out  of  the  sheets  without  fracture  and  without  even  stripping 
the  thread  of  either  the  external  or  the  internal  screw  :  this 
effect  was  due  partly  to  the  great  extension  of  the  metal,  which 
enlarged  the  holes,  and  partly  to  a  rolling  out  of  the  metal  as 
the  bolts  drew  from  their  sockets  in  the  sheet. 

Lines  of  uniform  extension  seemed  to  be  indicated  by  a 
peculiar  set  of  curved  lines  cutting  the  surface  scale  of  oxide  on 


STEAM-BOILER  EXPLOSIONS. 


641 


the  inner  surface  of  each  sheet,  and  resembling  closely  the  lines 
of  magnetic  force  called  by  physicists  magnetic  spectra. 
These  curious  markings  surrounded  all  of  the  stay-bolt  holes. 

The  third  experiment  took  place  at  a  later  date.  The 
boiler  selected  on  this  occasion  was  a  "  return-tubular  boil- 
er" with  no  lower  flues,  the  furnace  and  combustion-chamber 
occupying  the  whole  lower  part.  Its  surface  extended  the 
whole  width  of  the  boiler,  thus  giving  an  immense  crown-sheet. 

This  boiler  was  built  in  1845,  and  had  been  at  work  twenty- 
five  years ;  when  taken  out,  the  inspector's  certificate  allowed 
30  pounds  of  steam.  In  September  it  was  subjected  to  hydro- 
static pressure,  which  at  42  pounds  broke  a  brace  in  the  crown- 
sheets,  and  at  60  pounds  12  of  the  braces  over  the  furnace  gave 
way,  and  allowed  so  free  an  escape  of  water  as  to  prevent  the 
attainment  of  a  higher  pressure.  The  broken  parts  were  care- 
fully repaired,  and  the  boiler  again  tested  at  Sandy  Hook  to  59 
pounds,  which  was  borne  without  injury,  and  afterward  a  steam- 
pressure  of  45  pounds  left  it  still  uninjured.  At  the  final  ex- 
periment the  water-level  was  raised  to  the  height  of  15  inches 
above  the  tubes,  and  it  there  remained  to  the  end.  The  fire 
was  built,  as  in  the  previous  experiments,  with  as  much  wood  as 
would  burn  freely  in  the  furnace,  and  the  record  of  pressures  was 
as  follows: 


TIME. 

PRESSURE. 

TIME. 

PRESSURE. 

TIME. 

PRESSSURE. 

12.21  P.M. 
12.23  '*' 
12.25 

29^  Ibs. 

331    " 
371    " 

12.27  P'M- 
12.29      " 
12.31 

41  Ibs. 

12.32  P.M. 

12.33      " 
12.34 

50  Ibs.,  brace  broke. 

52    " 
53i  "     exploded. 

In  these  second  and  third  experiments  we  have  illustra- 
tions of  the  comparatively  rare  cases  in  which  explosions 
actually  occur. 

The  second  was  a  perfectly  new  construction,  in  which  cor- 
rosion had  not  developed  a  point  of  great  comparative  weak- 
ness, and  the  edges  yielding  along  the  lines  of  riveting  on  all 
sides  simultaneously  and  very  equally,  the  two  halves  were  com- 
pletely separated,  and  thrown  far  apart  with  all  of  the  energy  of 
41 


642  THE   STEAM-BOILER. 

unmistakable  explosion,  although  there  was  an  ample  supply  of 
water,  and  the  pressure  did  not  exceed  that  frequently  reached  in 
locomotives  and  on  the  western  rivers,  and  although  the  boiler 
itself  was  quite  diminutive. 

In  the  third  experiment  as  in  the  second  it  is  probable  that 
the  weakest  part  extended  very  uniformly  over  a  large  part  of 
the  boiler,  either  in  lines  of  weakened  metal,  or  over  surfaces 
largely  acted  upon  by  corrosion.  Immediately  upon  the  giving 
way  of  its  braces,  fracture  took  place  at  once  in  many  different 
parts. 

295.  Conclusions. — We  may  conclude,  then,  from  the  result 
of  Mr.  Stevens'  experiments  : 

First.  That  "  low-water,"  although  undoubtedly  one  cause, 
is  not  the  only  cause  of  violent  explosions,  as  is  so  commonly 
supposed  ;  but  that  a  most  violent  explosion  may  occur  with  a 
boiler  well  supplied  with  water,  and  in  which  the  steam-pressure 
is  gradually  and  slowly  accumulated. 

This  was  shown  on  a  small  scale  by  the  experiments  of  the 
committee  of  the  Franklin  Institute  above  referred  to. 

Second.  That  what  is  generally  considered  a  moderate  steam- 
pressure  may  produce  the  very  violent  explosion  of  a  weak 
boiler,  containing  a  large  body  of  water,  and  having  all  its  flues 
well  covered. 

This  had  never  before  been  directly  proven  by  experiment. 

Third.  That  a  steam-boiler  may  explode,  under  steam,  at  a 
pressure  less  than  that  which  it  had  successfully  withstood  at 
the  hydrostatic  test. 

The  last  boiler  had  been  tested  to  59  pounds,  and  after- 
ward exploded  at  53^  pounds.  This  fact,  too,  although  fre- 
quently urged  by  some  engineers,  was  generally  disbelieved. 
It  was  here  directly  proven.* 

*  A  number  of  instances  of  this  kind,  though  not  always  producing  an  explo- 
sion, have  been  made  known  to  the  Author.  Two  boilers  at  the  Detroit  Water 
Works,  in  1859,  after  resisting  the  hydrostatic  test  of  200  pounds  with  water,  at 
a  temperature  of  100°  Fahr.,  broke  several  braces  each  at  no  and  115  pounds 
steam-pressure  respectively,  when  first  tried  under  steam.  The  boiler  of  the  U. 
S.  steamer  Algonquin  was  tested  with  150  pounds  cold-water  pressure,  and  broke  a 
brace  at  100  pounds  when  tried  with  steam.  A  similar  case  occurred  in  New 
York  a  few  years  ago,  and  the  boiler  exploded  with  fatal  results.  These  acci- 


STEAM-BOILER  EXPLOSIONS.  643 

In  addition  to  the  deductions  summarized  above,  the 
Author  would  conclude — 

Fourth.  That  the  violence  of  an  explosion  under  gradually 
accumulating  pressures  is  determined  largely  by  the  nature  of 
the  injury  and  the  extent  of  the  primary  rupture  due  to  it. 
A  merely  local  defect  or  failure  would  not  be  likely  to  cause 
explosion. 

Fifth.  That  the  overheating  of  the  metal. of  a  boiler  in  con- 
sequence of  low-water  may  or  may  not  produce  explosion,  ac- 
cordingly as  the  sheet  is  more  or  less  weakened  or  as  the 
amount  of  steam  made  on  the  overflow  of  the  dry  heated  area 
by  water  is  greater  or  less. 

Sixth.  That  the  superheating  of  either  water  or  steam  is 
not  to  be  considered  a  probable  cause  of  explosions. 

Seventh.  That  the  question  whether  the  repulsion  of  water 
from  a  plate  by  the  overheating  of  the  latter  may  occur  with 
resulting  explosion  remains  unsettled  ;  but  that  it  is  certain 
that  the  number  of  explosions  attributable  to  this  cause  is 
comparatively  small. 

Eighth.  That  all  explosions  are  certainly  due  to  simple  and 
preventable  causes,  and  nearly  all  to  simple  ignorance  or  care- 
lessness, on  the  part  of  either  designer,  constructor,  proprietor, 
or  attendants. 

A  committee  of  the  British  House  of  Commons,  after  long 
study  and  careful  investigation  of  this  subject,  made  the  fol- 
lowing recommendations  : 

(a)  That  it  be  distinctly  laid  down  by  statute  that  the 
steam-user  is  responsible  for  the  efficiency  of  his  boilers  and 
machinery,  and  for  employing  competent  men  to  work  them  ; 
($)  that,  in  the  event  of  an  explosion,  the  onus  of  proof  of 
efficiency  should  rest  on  the  steam-user ;  (c)  that  in  order  to 
raise  prima-facie  proof,  it  shall  be  sufficient  to  show  that  the 
boiler  was  at  the  time  of  the  explosion  under  the  management 
of  the  owner  or  user,  or  his  servant,  and  such  prima-facie 
proof  shall  only  be  rebutted  by  proof  that  the  accident  arose 

dents  are  probably  caused  by  changes  of  forrri  of  the  boiler,  under  varying  tem- 
perature, which  throw  undue  strain  upon  some  one  part,  which  may  have  already 
been  nearly  fractured. 


644  THE   STEAM-BOILER. 

from  some  cause  beyond  the  control  of  such  owner  or  user ; 
and  that  it  shall  be  no  defence  in  an  action  by  a  servant  against 
such  owner  or  user  being  his  master,  that  the  damage  arose 
from  the  negligence  of  a  fellow-servant. 

The  Prevention  of  steam-boiler  explosions  is  now  seen  to 
be  a  matter  of  the  utmost  simplicity.  A  well-designed,  well- 
made  and  set,  and  properly  managed  steam-boiler  may  be  con- 
sidered as  safe.  Explosions  never  occur  in  such  cases.  To 
secure  correct  design  and  proportions,  a  competent  engineer 
should  be  found  to  make  the  plans  ;  to  obtain  good  construc- 
tion, a  reliable,  intelligent  and  experienced  maker  must  be 
intrusted  with  the  construction  under  proper  supervision  and 
precise  instructions  from  the  designer ;  and  the  latter  should 
also  attend  carefully  to  the  installation  of  the  boiler.  In  order 
to  insure  good  management,  trustworthy,  skilful,  and  experi- 
enced attendants  must  be  found,  who,  under  definite  instruc- 
tions, may  at  all  times  be  depended  upon  to  do  their  work 
properly.  Periodical  inspection,  prompt  repair  of  all  defects 
when  discovered,  and  the  removal  of  the  boiler  before  it  has 
become  generally  deteriorated  and  unreliable  are  absolute  safe- 
guards against  explosion. 


APPENDIX. 


646 


THE  STEAM-BOILER. 


NOTE.—  The  following  table  gives  the  data  required  by  the  engineer  in  this  connection  as  based  upon  the  experiments  of  Regnault  The  tempera- 
es,  pressures,  and  heat-measures  are  all  from  Regnault's  experiments.  The  other  quantities  were  calculated  by  Mr.  R  H  Buel  *  adopting  thefor- 
las  of  Rankme  already  given  to  obtain  quantities  not  ascertained  by  direct  experiment.  The  two  parts  of  the  latent  heat  of  vaporization  are  separately 
ermined,  and  the  internal  thus  distinguished  from  the  external  work  of  expansion.  British  measures  are  adopted.  The  nomenclature  is  sufficientlv 
1  explained  by  the  table-  headings. 

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647 


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APPENDIX. 


649 


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650 


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APPENDIX. 


65I 


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H 

THE   STEAM-BOILER. 


The  column  headed  "  U"  in  the  table  of  the  properties  of 
saturated  steam  is  useful  for  reducing  the  performance  of  differ- 
ent boilers  to  a  common  standard — this  standard  being  that 
most  generally  accepted  by  engineers :  the  equivalent  evapora- 
tion at  atmospheric  pressure  and  the  temperature  of  boiling 
water,  or,  as  it  is  frequently  called,  the  evaporation  from  and  at 
212°.  In  the  table  it  is  assumed  that  the  temperature  of  the 
feed-water  is  32°,  and  an  auxiliary  table  is  added,  giving 
corrections  for  any  temperature  of  feed  from  32°  to  212°. 

CORRECTION  FOR  TOTAL  HEAT  IN  UNITS  OF  EVAPORATION. 


Tempera- 
ture of 
feed,  Fah- 
renheit 
degrees. 

Correction. 

Tempera- 
ture of 
feed,  Fah- 
renheit 
degrees. 

Correction. 

Tempera- 
ture of 
feed,  Fah- 
renheit 
degrees. 

Correction. 

Tempera- 
ture of 
feed,  Fah- 
renheit 
degrees. 

Correction. 

Tempera- 
ture of 
feed,Fah 
renheit 
degrees. 

Correction. 

33 

.0010 

69 

.0383 

I05 

.0756 

141 

.1129 

177 

.1504 

34 

.0021 

70 

•0393 

106 

.0766 

142 

.1140 

178 

•1514 

35 

.0031 

7i 

.0404 

107 

.0777 

M3 

.1150 

179 

•  1525 

36 

.0041 

72 

.0414 

108 

.0787 

144 

.1160 

180 

•1535 

37 

.0052 

73 

.0424 

109 

.0797 

MS 

.1171 

181 

•I545 

38 

.0062 

74 

•0435 

no 

.0808 

146 

.1181 

182 

-1556 

39 

.0073 

75 

•0445 

III 

.0818 

i47 

.  1192 

183 

.1566 

40 

.0083 

76 

.0450 

112 

.0829 

148 

.1202 

184 

•!577 

4i 

.0093 

77 

.0466 

"3 

.0839 

149 

•1213 

185 

•1587 

42 

.0104 

78 

.0476 

114 

.0849 

150 

.1223 

186 

.1598 

43 

.0114 

79 

.0487 

"5 

.0860 

151 

•1233 

187 

.1608 

44 

.0124 

80 

•0497 

116 

.0870 

152 

.1244 

1  88 

.1618 

45 

•0135 

81 

.0507 

117 

.0880 

i53 

•1254 

189 

.1629 

46 

.0145 

82 

.0518 

118 

.0891 

i54 

.1264 

190 

.1639 

47 

•0155 

83 

•  0528 

119 

.0901 

155 

•1275 

191 

•  165° 

48 

.0166 

84 

.0538 

120 

.0911 

156 

.1285 

192 

.1660 

49 

.0176 

85 

•0549 

121 

.0922 

i57 

.1296 

193 

.1670 

50 

.0186 

86 

•0559 

122 

.0932 

158 

.  1306 

194 

.1681 

51 

.0197 

87 

.0569 

123 

•0943 

159 

.1316 

*95 

.  1691 

52 

.0207 

88 

.0580 

124 

•0953 

160 

•1327 

196 

.1702 

53 

.0217 

89 

.0590 

I25 

.0963 

161 

•I337 

.1712 

54 

.0228 

90 

.0601 

126 

.0974 

162 

.1348 

198 

•X723 

55 

.0238 

91 

.0611 

I27 

.0984 

163 

.1358 

199 

•r733 

56 

.0248 

92 

.0621 

128 

.0994 

164 

.1368 

200 

•I743 

% 

.0259 
.0269 

93 
94 

.0632 
.0642 

I29 
I30 

.1005 
.1015 

3' 

•1379 
.1389 

201 
2O2 

•1754 
.1764 

59 

.0279 

95 

.0652 

131 

.1025 

i67 

.1400 

203 

•I775 

60 

.0290 

96 

.0663 

I32 

.1036 

168 

.  1410 

204 

•1785 

61 

.0300 

97 

.0673 

133 

.  1046 

169 

.1420 

205 

.1796 

62 
63 

.0311 
.0321 

98 
90 

.0683 
.0694 

T34 
135 

•1057 
.  1067 

170 
171 

•I43i 
.1441 

206 
207 

.1806 
.1817 

64 

•OSS1 

100 

.0704 

136 

.1077 

172 

•1452 

208 

.1827 

6| 

.0342 

101 

.0714 

137 

.1088 

173 

.  1462 

209 

•1837 

66 

.0352 

102 

.0725 

138 

.1098 

J74 

•I473 

210 

.1848 

67 

.0362 

I03 

•°735 

139 

.1109 

175 

.1483 

211 

.1858 

68 

.0372 

I04 

.0746 

140 

.1119 

176 

•1493 

212 

.1869 

\PPENDIX. 


653 


TABLE    la. 

TEMPERATURES  AND  PRESSURES,  SATURATED  STEAM. 
IN  METRIC  MEASURES  AND  FROM   REGNAULT. 


£ 

jj 

1 

QJ 

STEAM-PRESSURE. 

fll 

STEAM-PRESSURE. 

S 

e 

V 

In  Centimetres. 

In  Atmospheres 

a 
6 
0 

In  Centimetres. 

In  Atmospheres 

t_l 

H 

-  32°  c 

0.0320 

0.0004 

'+  14°  C 

.1908 

0.016 

31 

0.0352 

0.0005 

15 

.2699 

0.017 

30 

0.0386 

0.0005 

16 

•3536 

0.018 

29 

0.0424 

O.OOO6 

17 

.4421 

o.org 

28 

o  .  0464 

0.0006 

18 

•5357 

O.O2O 

27 

0.0508 

0.0007 

19 

.6346 

0.022 

26 

0.0555 

o  .  0007 

20 

•7391 

0.023 

25 

0.0605 

O.OOOS 

21 

.8495 

0.024 

24 

o  .  0660 

O.OOOg 

22 

•9659 

0.026 

23 

0.0719 

O.OOOg 

23 

2.0888 

0.028 

22 

0.0783 

O.OOIO 

24 

2.2184 

0.029 

21 

0.0853 

O.OOII 

25 

2.3550 

0.031 

20 

0.0927 

0.0012 

26 

2.4988 

0.033 

19 

0.1008 

O.OOI3 

27 

2.5505 

0.034 

18 

0.1095 

O.OOI4 

28 

2.8101 

0.037 

17 

o.  1189 

0.0015 

29 

2.9782 

0.039 

16 

0.1290 

O.OOI7 

30 

3-1548 

0.042 

15 

o  .  1400 

O.OOlS 

31 

3.3406 

0.044 

14 

0.1518 

O  .  OO2O 

32 

3-5359 

0.047 

13 

0.1646 

0.0022 

33 

3-74H 

0.049 

12 

0.1783 

o  .  0024 

34 

3-9565 

0.052 

II 

0.1933 

0.0025 

35 

4.1827 

0.055 

10 

0.2093 

0.0027 

36 

4.4201 

0.058 

9 

0.2267 

o  .  0030 

37 

4.6691 

0.061 

8 

0.2455 

0.0032 

38 

4.9302 

0.065 

7 

0.2658 

O.OO35 

39 

5.2039 

0.068 

6 

0.2876 

0.0038 

40 

5.4906 

0.072 

5 

0.3113 

0.0041 

4i 

5-791° 

0.076 

4 

0.3368 

0.0044 

42 

6.1055 

0.080 

3 

0.3644 

0.0048 

43 

6.4346 

0.085 

2 

0.3941 

0.0052 

44 

6.7790 

0.089 

I 

0.4263 

O.OO56 

45 

7-I391 

0.094 

O 

0.4600 

0.0061 

46 

7.5158 

0.099 

+    I 

0.4940 

0.0065 

47 

7.9093 

o.  104 

2 

0.5302 

0.0070 

48 

8.3204 

0.109 

3 

0.5687 

0.0073 

49 

8.7499 

0.115 

4 

o  .  6097 

0.0080 

50 

9.  1982 

O.I2I 

5 

0.6534 

0.0086 

5i 

9.6661 

O.I27 

6 

0.6998 

0.0092 

52 

10.1543 

0.134 

7 

0.7492 

0.0199 

53 

10.6636 

O.I4O 

8 

0.8017 

0.0107 

54 

11.1945 

0.147 

9 

0.8574 

O.OII 

55 

11.7478 

0.155 

10 

0.9165 

O.OI2 

56 

12.3244 

0.163 

ii 

0.9792 

0.013 

57 

12.9251 

0.170 

12 

1.0457 

0.014 

58 

13.5505 

0.178 

13 

1.1162 

0.015 

59 

14.2015 

0.187 

654 


THE   STEAM-BOILER. 


TABLE    la.— Continued. 


ti 

u 

a 

STEAM-PRESSURE. 

3 

STEAM-PRESSURE. 

e 

1 

1 

d. 

i 

In  Centimetres. 

In  Atmospheres 

B 

<u 

In  Centimetres. 

In  Atmospheres 

H 

H 

+  60°  c. 

14.8791 

0.196 

+iio°C 

107-537 

.415 

61 

15.5839 

0.205 

in 

111.209 

•463 

62 

16.3170 

0.215 

112 

114.983 

•513 

63 

17.0791 

0.225 

113 

118.861 

.564 

64 

17.8714 

0.235 

114 

122.847 

.616 

65 

18.6945 

0.246 

115 

126.941 

.670 

66 

19.5496 

0.257 

116 

I3LI47 

.726 

67 

20.4376 

0.267 

117 

135.466 

.782 

68 

21.3596 

0.281 

118 

I39.902 

.841 

69 

22.3165 

0.294 

119 

144-455 

.901 

70 

23  •  3093 

0.306 

120 

149.128 

.962 

71 

24-3393 

0.320 

121 

153.925 

2.025 

72 

25-4073 

0.334 

122 

158.847 

2.091 

73 

26-5147 

0-349 

123 

163.896 

2.157 

74 

27.6624 

0.364 

124 

169.076 

2.225 

75 

28.8517 

0.380 

125 

174.388 

2.295 

76 

30.0838 

0.396 

126 

I79.835 

2.366 

77 

31.3600 

0.414 

127 

185.420 

2.430 

78 

32.6811 

0.430 

128 

191.147 

2.515 

79 

34.0488 

0.448 

I29 

197.015 

2.592 

80 

35.4643 

0.466 

130 

203.028 

2.671 

81 

36.9287 

0.486 

131 

209.194 

2.753 

82 

38.4435 

o.  506 

132 

2I5-503 

2.836 

83 

40  oroi 

0.526 

133 

221.969 

2.921 

84 

41.6298 

0.548 

134 

228.592 

3.008 

85 

43-304I 

0.570 

135 

235-373 

3.097 

86 

45  0344 

0-593 

136 

242.316 

3.188 

87 

46.8221 

0.616 

137 

249.423 

3.282 

88 

48.6687 

0.640 

138 

256.700 

3-378 

89 

50-5759 

0.665 

139 

264.144 

3.476 

90 

52,5450 

0.691 

140 

271-763 

3-576 

91 

54*5778 

0.719 

141 

279-557 

3.678 

92 

56.6757 

0.746 

142 

287.530 

3.783 

93 

58.8406 

0-774 

143 

295.686 

3.890 

94 

61.0740 

0.804 

144 

304  .  026 

4.000 

95 

63.3778 

0.834 

M5 

312.555 

4-II3 

96 

65-7535 

0.865 

146 

321.274- 

4.227 

97 

68.2029 

0.897 

147 

330.187 

4-344 

98 

70.7280 

0.931 

I48 

339.  298 

4.464 

99 

73.3305 

0.965 

149 

348  .  609 

4.587 

IOO 

76  ooo 

.000 

150 

358.123 

4.712 

101 

76.7590 

.036 

367.843 

4.840 

102 

81.6010 

.074 

152 

377-774 

4.971 

103 

84.5280 

.112 

153 

387.918 

5.104 

104 

87.5410 

.152 

154 

398.277 

5-240 

105 

90  6410 

•193 

155 

408.856 

5.380 

106 

93.8310 

235 

156 

419.659 

5-522 

107 

97.1140 

.278 

157 

430.688 

5.667 

1  08 

loo  4910 

-322 

I58 

44L945 

5-815 

109 

103  965 

-368 

159 

453.436 

5.966 

APPENDIX. 
TABLE    \a. — Continued. 


655 


3 

STEAM-PRESSURE. 

3 

STEAM-PRESSURE. 

2 

rt 

a 

a 
I 

In  Centimetres. 

In  Atmospheres 

a 
1 

In  Centimetres. 

In  Atmospheres 

4-  1  60°  a 

465.  162 

6.I2O 

4-196°  c. 

1074.595 

14.139 

161 

477.128 

6.278 

197 

1097.500 

14.441 

162 

489.336 

6.439 

198 

1120.982 

14  .  749 

163 

501.791 

6.603 

199 

1144.746 

15.062 

164 

514.497 

6.770 

200 

1168.896 

15-380 

165 

527.454 

6.940 

201 

H93.437 

15.703 

1  66 

540.669 

7.114 

2O2 

1218.369 

16.031 

167 

554.143 

7.291 

2O3 

1243.700 

16.364 

168 

567.882 

7.472 

204 

1269.430 

16.703 

169 

581.890 

7.656 

205 

1295.566 

17.047 

170 

596.  1  66 

7.844 

206 

1322.  112 

17.396 

171 

610.719 

8.036 

207 

I349.075 

17.751 

1J2 

625.548 

8.231 

208 

1376.453 

18.111 

173 

640  .  660 

8-430 

2O9 

1404.252 

18.477 

174 

656.055 

8.632 

2IO 

1432.480 

18.848 

175 

671.743 

8.839 

211 

1461.132 

19.226 

176 

687.722 

9.049 

212 

I49O.222 

19.608 

177 

703.997 

9.263 

2I3 

1519.748 

19.997 

178 

720.572 

9.481 

2I4 

1549.717 

20.391 

179 

737-452 

9-703 

215 

1580.133 

20.791 

180 

754.639 

9-929 

216 

1610.994 

21.197 

181 

772.137 

10.150 

217 

1642.315 

2  1  .  690 

182 

789.952 

10.394 

218 

1674.090 

22.027 

183 

808.084 

10.633 

2I9 

1706.329 

22.452 

184 

826.540 

10.876 

220 

I739.036 

22.882 

185 

845-323 

11.123 

221 

1772.213 

23.319 

186 

864.435 

n.374 

222 

1805.864 

23.761 

187 

883.882 

11.630 

223 

1839.994 

24.2IO 

1  88 

903.668 

11.885 

224 

1874-607 

24.666 

189 

923  •  795 

12.155 

225 

1909.704 

25.128 

190 

944.270 

12.425 

226 

1945.292 

25.596 

191 

965-093 

12.699 

227 

1981.376 

26.071 

192 

986.271 

12.977 

228 

2017.961 

26.552 

193 

1007  .  804 

13.261 

229 

2055.048 

27.040 

194 

1029.701 

13.549 

230 

2092.640 

27-535 

195 

1051.963 

13-842 

656 


THE   STEAM-BOILER. 


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INDEX. 


A 

SEC.  PAGE 

Air,  minimum,  required  in  Fire, 77  178 

Anthracite  Coals,          . 64  155 

Apparatus,  forms  of  gas-analysis 265  531 

Applications  of  Boilers         .         .         .         .                  .         .         .14  20 

Appurtenances  of  Steam  Boilers, 10  18 

Area  of  Cooling  Surfaces,  formulas  for,        .         .        .                 .98  221 


B 

Barrel  Calorimeters,  forms  of,     .        . 260  519 

use  of, 260  519 

Bituminous  Coals,         .         .         .         .         .         .         .         .                65  156 

Bodies,  molecular  constitution  of,        .         .        •        •        •        .     109  241 

Boiler,  common  proportions  and  Work  of,  .         .         .         .         .     161  335 

conditions  of  efficiency  of, 149  303 

design  of  Plain  Cylinder, . 169  350 

determination  of  Value  of,         .         .                 .         .        .     246  485 

form  and  Location  of  Bridge-wall  of,       ....     179  381 

forming  bent  parts  of, 190  403 

general  decay  of,                         .                  .         .        .         .     288  604 

management  of,  . 206  440 

local  decay  of,  .         . .     288  604 

matters  of  detail  of,           ....         .         .         .168  346 

number  of, 164  340 

office  of  the  Steam,  ....         .                  .         .         i  i 

operation  of,     .         .         .         .         .         ...         .     212  445 

parts  of,  denned,      . 168  346 

selection  of  Type  and  location  of,    .         .         .         .         .14?  300 

size  of,      .         ....         .         .         .         .         .164  340 

the  Locomotive,        ......         .         .         .16  26 

transfer  of  Heat  in  the  Steam,          .         .         .         .         -97  220 

The  older  Types  of,          .       '  .       •  .         .         .         .         .         3  4 

The  Scotch,      .         ..'.-...        .        •     ,  *9  32 

Upright  and  portable,    •  .                   ._-.-.         .         .175  3^9 

Boiler-construction,  controlling  ideas  in,      .         .         .         .         .     151  3°7 


660  INDEX. 

SEC.  PAGE 

Boiler-Design,  details  of  the  problem  of,     .         .         .         ,              166  345 

general  consideration  of,       .....     167  346 

principles  of,          .         .         .         .         .         .         .150  304 

problem  stated,     .......     164  340 

special  conditions  affecting,           .         .         .         .156  317 

Boiler-Power,        ..........     164  340 

Boiler-pressure,  choice  of,    .         .         .         .         .         .         .         .     149  303 

Boiler- trials,  errors  of, 262  521 

precautions  observed  at,  .         .         .         .         .         .     257  514 

purposes  of,      ........     244  484 

record-blanks  for.    .         ...         .         .         .         .     257  514 

records  of,        ........     262  521 

Boilers,  appurtenances  of  Steam,         .        .        ......         .10  18 

assembling  of,          ........     194  420 

classification- of,       ........        u  19 

common  "  Shell "  stationary, 15  21 

corrosion  of,  .........     287  601 

cost  of, 152  311 

covering  of,     .         .         .         .         .         .         .         .         .178  380 

coverings  of,  .........     227  456 

cylindrical  Tubular 171  358 

defects  of  construction  of,       ......     286  596 

design  of,        .         .         .         .         .         .         .285  593 

deterioration  of 57  144 

developed  weakness  of,  .         .         .         .         ».'..«         •     287  601 

drawings  of  construction  of,    .         .         ,         .         .         .186  400 

efficiency  of ,                        152  311 

efficiency  of  the  Steam 234  472 

energy  stored  in,     ........     269  541 

factors  of  safety  for,        .......     152  311 

general  care  of,        ........     222  454 

general  instructions  in  management  of,          ...     233  469 

Horse-power  of,      ........     145  292 

inspection  of,  .........     195  420 

inspection  and  test  of,  .....       56,  232     140.  466 

management  of, 291  612 

Marine  Flue, 172  361 

Marine;  older-forms.     .         .         .         .         .         .         .17  29 

Marine  Sectional,    ........       21  38 

Marine  Tubular, 173  362 

Marine  Water-tube,         .......       18  30 

Methods  of  construction  of,    ...          ...     186  400 

corrosion  in,         .         .         .         .         .         .     289  606 

decay  in,       .......     289  606 

of  locomotives ,     177  377 

periods  of  introduction  of, 22  39 


INDEX.  66 1 


Boilers,  power  of,         ........ 

SEC. 

.     144 

PAGE 
29I 

problems  in  the  use  of,    . 

•       25 

43 

processes  of  construction  of  ,  .         .         .         . 

1  86 

400 

relative  security  of, 

.    284 

'      592 

relative  strength  of  Shell  and  Sectional, 

•      58 

148 

relative  value  of,     

.    250 

488 

repairs  of,        ........ 

.    231 

465 

sectional,         ........ 

20 

33 

.     174 

364 

setting  of,        ........ 

•     177 

369 

special  forms  of,     

•       23 

42 

shells  of,           

•       55 

129 

.       202 

427 

stationary  Flue,       ....... 

.       170 

354 

.       I92 

413 

Steam,  explosions  of,               .         .         .         ... 

.       268 

538 

suspension  of,          .                   

•       177 

377 

testing  Steam,          .         .         .         .  •      . 

.       I96 

422 

transportation  and  delivery  

.       198 

424 

Braced  and  Stayed  Surfaces,         

.         60 

151 

•       54 

127 

.     179 

38i 

Bursting  

.     271 

549 

c 

Calorimeters,  Theory  of, 261  521 

Calorimetry,          ..........  92  214 

Calking  and  chipping,  .         .         .         .         .         .         .         .         .  193  417 

Charcoal, .70  162 

Chemical  characteristics  of  Iron,          ......  30  57 

Chimney  Draught,        .........  157  317 

Forms  of.      .........  158  322 

Flues,  and  Grate,  relative  areas  of,                         .         .  160  334 

size  of.  ..........  158  322 

Chipping  and  Calking,           ........  193  417 

Coal  Calorimeter,  The,         ........  263  524 

defined,         .         .         .         .         .         .         .         .         .         .63  153 

Coals,  anthracite,          , 64  155 

Bituminous, 65  156 

Coke, 69  160 

Colburn's  Theory  of  Explosions, 275  559 

Combustion  defined  :  Perfect  combustion, 62  152 

efficiency  of, 236  473 

method  of 148  302 

rate  of, 79  184 

temperature  of  products  of, 78  179 


662  INDEX. 

SEC.  PAGE 

Commercial  efficiency,         .         .         .         .         •    *     .         .         .     240  474 

theory  of,        ....        .         .     242  477 

Conclusions  relating  to  explosions,      .         .                  .         .         .     295  642 

Construction  of  Boilers,  defective,       .         .         .         .         .         .     286  596 

Construction,  problem  in  Design  and, 24  43 

Continuous  Calorimeters,  The,             .....         .         .     263  524 

Contract,      .         . •    .         .     200  426 

purpose  of  Specification  and,   .     .         •••••'.         .     199  425 

Cooling  Surfaces,  Area  of,  Formulas  for,    .        .         .         .         .98  221 

Copper,        .         ...........         .       54  I27 

Corrosion,  chemistry  of,       .        .         ...         .     -    .        .         .     223  454 

method  of,           .........         .         .     224  455 

methods  of,  in  Boilers,       ...        •*         .        .     289  606 

of  Boilers,  ......                  .              287  601 

Critical  Point,       .         .         .         .....         .         .129  265 

Crystallization  and  Granulation 37  9° 

Curves  of  Energy,         .........     143  289 

Cylindrical  Tubular  Boilers,         .•                         .        .        .         .171  358- 


D 

Dampers,  location  and  Form  of .181  381 

Decay,  general,  of  ^Boilers,  .......  288  604 

local,  of  Boilers, 288  604 

Methods  of,  in  Boilers,    .                  .         ...         .  289  606 

Delivery  of  Boilers,       .....                  ...  198  424 

Deposits,  Incrustation  and  effect  of 99  218 

Design  and  construction,  problems  in,         .....  24  43 

of  Boilers,  special  conditions  affecting,  ....  156  317 

defects  of, 285  593 

Designing  Boilers,  principles  involved  in, 6  n 

Deterioration  of  Boilers,      ........  57  144 

Donny  and  Dufour,  experiments  of,    .         .         ...         .281  578 

Draught  Gauges, .         .  267  535 

natural  and  forced,         .......  155  314 

Drilling  and  punching, 189  402 

Ductility,      ...........  29  56 

of  Metal,  loss  of, 59  149- 

E 

Economy,  relation  of  Area  of  Heating  Surface  to,      .        .        .  252  490 

Efficiency  and  Quantity  of  Steam,         .                  .     -  .         .         .  163  338 

as  indicated  by  Gas-analysis,       .....  216  449 

combined  power  and  .......  253  489 


INDEX. 

SEC. 

Efficiency,  commercial, 240 

finance  of, 239 

measures  of,         ........  235 

of  Boiler,  conditions  of,       .         .         .         .         .         .  149 

of  Heating  surfaces,  Formulas  for,     ....  98 

Theory  of  commercial,         ......  242 

Efficiency,  variations  of,  with  consumption  of  Fuel  and  size  of 

grate, 251 

Efficiencies,  algebraic  Theory  of, 241 

Elasticity,      ...         ........  29 

Emergencies,         .........     217,  229 

Energetics;    Heat-energy  and  Molecular  Velocity,      .         .         .  101 

Energy,  curves  of,        .........  143 

Heat  and  Mechanical,     .......  105 

Heat  as  a  form  of,  .         . 98 

of  Steam  alone,        .         .         .         .         .         .         .         .  270 

stored,  in  Steam,     .         .         ...         .         .         .  142 

stored,  in  Boilers,  ........  269 

heated  Metal, 277 

superheated  Water,         .         .        .         .         .281 

Evaporation,  factors  of, 139 

usual  rate  of, 162 

Excess  of  Pressure,      .........  221 

Expansion,  Latent  Heat  of,          .         .         .         .         .         .         .113 

Experimental  explosions  and  investigations,        ....  294 

Experiments  of  Donny  and  Dufour, 281 

Leidenfrost  and  Boutigny,  .....  282 

Explosions,  absurd,  causes  of,                        272 

causes  of, 272,  293 

Colburn's  Theory  of,         ......  275 

definition  of 271 

description  of, 271 

examples  of, 293 

experimental 294 

fulminating,       ........  271 

improbable  causes  of,        ......  272 

Lavvson's  and  others'  experiments  of,       ...  276 

methods  of,  .     .         .         .         .         .         .         .         .  274 

of  Steam-boilers, 268 

possible  causes  of, 272 

probable  causes  of, 272 

results  of,  .                  293 

statistics  of  causes  of, 273 

Theories  of, 274 

usual  causes  of,          .                                    ...  272 


664  INDEX. 

F 

SEC.  PAGE 

Feed  apparatus, i§4  392 

Filtration,     .                  124  260 

Fitting,          .                           188  402 

Fire,  minimum  air  required  in,     .......  77  J7S 

temperature  of,    .........  76  I/2 

•Fire-rooms,  closed  and  open,        .......  214  448 

Fire-tubes, 153  312 

Fires,  starting   of, 207  441 

the  management  of,    .         .         .         .                   .         .         •  208  442 

Flanging  and  Pressing, 189  402 

Flue-boilers,  Marine, 172  361 

stationary 170  354 

Flues,  Chimney  and  Grate,  relative  areas  of,       .         .         .         .  160  334 

collapsed 271  549 

disposition  of,    .         .         .         .         .         •         .         .         .  180  381 

flanged  and  corrugated,     .         .         .         .         .         .         -  61  151 

setting  of, 192  413 

Forced  Draught, 213  448 

Forces  and  Work,  computation  of  External,         .         .         .         .118  248 

Internal,         .         .         .         .118  248 

Form,  effect  of  variation  of, 32  64 

Forms  of  Boilers,  modern  standard, 12  20 

Fuel,  adaptation  of,       .........  88  206 

choice  of      ..........  148  302 

economy  of .         .81,  249    187,  487 

pulverized,  ..........  71  164 

test  of  Value  of 245  485 

use  of  various  kinds  of,        .......  209  444 

Fuels, 63  153 

analysis  of,         .........  248  486 

artificial, 74  168 

commercial  value  of,          .......  86  201 

composition  of,          ........  83  192 

efficiency  of,       .........  249  487 

evaporative  Power  of 247  485 

Gaseous,    ..........  73  167 

heating  effects  of,       ........  84  194 

heating-power  of,       ........  75  169 

liquid, 72  165 

and  Gaseous,  .         .         .         .         .         .         .         .210  444 

solid,          .         .         .         .         .         .         .         .         .         .211  445 

Furnace,  adaptation  of, 88  206 

and  grate,      .........  159  329 

efficiency  of, 80  185 

management,          ........  87  204 


INDEX.  665 

SEC.  PAGE 

Fusible  Plugs, 185  393 

Fusion  and  Vaporization,  latent  heats  of,     .        .        .        .             114  214 

G 

Galvanic  Action, 229  462 

Gas-analysis,  efficiency  as  indicated  by, 266  535 

Gases,  analysis  of, 265  531 

defined;  the  perfect  gas,  . no  241 

Gaseous  Fuels, -73  167 

Gauges,  draught,           .........     267  535 

Granulation  and  Crystallization,  .......       37  90 

Grate  and  Furnace,  .........  159  227 

Flues,  Chimney,  relative  areas  of 160  334 

Grooving  and  furrowing,  .  .  .  .  .  .  .  .  289  606 

H 

Heat,  as  a  form  of  energy, 100  229 

and  matter;  Specific  heat, in  242 

and  mechanical  Energy,  .......  105  237 

conduction-  of,  .  •  95  2I7 

convection  of,    .........       96  219 

efficiency  of  Transfer  of,  .         .         .         .    .     .         .         .237  473 

methods  of  Production  of,          .         .         .         .         .         .90  208 

nature  of,   .         .         .         .         .         .         .         .         .         .89  207 

production,  transfer,  and  strength  of,  ....  7  12 

quantities  of,  .  .  .  . 91  2I° 

radiation  of, 94  216 

Sensible  and  Latent,  .  .  .  .  .  .  .  .112  243 

Specific,  .  - 91  210 

transfer  of, 93  215 

in  Steam  Boilers, 97  200 

Transformations,  .  .  .  ,  .  .  •  .105  237 

utilization  of,  .  .  ...  .  .  .  .88  15 

Heat-energy,  as  related  to  Temperature, 102  235 

distribution  of,        .         .         .         .        .         .              115  244 

quantitative  measure  of, 103  236 

Heaters, 184  382 

Heating  effects  of  Fuels, 84  194 

power  of  Fuels,  ........  75  ^69 

Heating-surface  to  economy,  relation  of  area  of,  ...  252  489 

efficiency  of,  Formulas  for,  ....  98  221 

Heats,  computation  of  Latent  and  Total 138  276 

specific,  of  Steam  and  Water, 13?  275 

Total  and  Latent;  Internal  Pressures  and  Work,  .  .  133  271 

Helical  Seams, 49  "7 

Horse-power  of  Boilers, .     145  292 


666  INDEX. 


I 

SEC.  PAGE 

Improvement  in  Boilers,  method  and  limit  of,     ....         5  10 

Incrustation,         ..........     230  462 

Incrustation  and  Deposits,  effect  of, 99  228 

Sediment, 280  574 

Inspections  and  Test  of  Boilers,  .......       56  140 

Inspector,  duties  of  the 205  438 

Internal  Pressures  and  Work;  Total  and  Latent  Heats,.       .         .     133  271 

computation  of,     .         .         .         .     134  271 

Investigations  and  Experimental  explosions,       ,                                294  633 

Iron,  Cast  and  Malleableized, 54  127 

choice  of,  for  various  parts,         .        .         .         .         .        .44  112 

preservation  of,  .........     226  564 

Physical  and  Chemical  characteristics  of,  .         .         .         .30  57 

specification  of  quality  of, 43  108 

Iron  and  Steel  compared,     .........       38-  92 

durability  of,         .         ...         .         .         .         .     225  457 

method  of  Test  of,        . 41  98 

L 

Latent  and  sensible  heat,     .        .        ....        .        .        .112  243 

Heat  of  Expansion,  . 113  243 

Heats,  computation  of,     .         .         .         .         .         .         .     138  276 

of  Fusion  and  Vaporization, .         .         .        .         .114  244 

Lawson's  and  others'  Experiments,      ......     276  561 

Leakage,       ...........     228  461 

Leidenfrost's  and  Boutigny's  Experiments,          ....     282  583 

Lignites,       ...........       66  158 

Liquid  Fuels,        ..........       72  165 

Liquids  defined,  .         .         .         .         .         .         .         .         .         .no  241 

Location  and  Type  of  Boiler,  Selection  of,          ....     147  300 

Locomotive  Boiler,  The,      ........       16  26 

Boilers,    .........     176  371 

Low-water,  ...........     218  450 

causes  of,     .........     279  568 

consequences  of,          .......     279  568 

M 

Marine  Boilers,  older  Forms, 17  29 

Flue  Boilers,     .........     172  361 

Tubular  Boilers,       ........     173  362 

Water-tube  Boilers, 18  30 

Materials  required,  Quantity  of,  .......       27  45 

Metal,  heated,  energy  stored  in,  .         .                  »                  .         .     277  567 

loss  of  Strength  and  Ductility  of,     .        .        .         .         -59  *49 


INDEX.  667 

SEC.  PAGE 

Methods  of  Explosions,        .         ...         .         •         .         .         .  274  558 

Method  of  Treatment,  effect  of, 33  70 

Minor  accessories,         . 185  393 

Mixed  applications  of  Boilers, 14  20 

Types  of  Boilers 13  20 

Molecular  constitution  of  Bodies, 109  241 

•    N 

Net  efficiency, 238  473 

Number  of  Boilers, 164  340 

O 

Operation  of  Boilers,  safety  in 9  18 

Overstrain,  method  of  detecting, 35  81 

P 

Paints  and  Preservatives, 227  458 

Peat  or  Turf 67  159 

Physical  characteristics  of  Iron, 30  57 

State  of  Water,  changes  of, 128  265 

Pipes,  Steam  and  Water, 182  383 

Plain  Cylinder  Boiler,  design  of, 169  350 

Planing, 188  402 

Plant,  efficiency  of  a  given,          .......  243  481 

Plate,  Grades  and  Quantities  of  Iron  in  Boilers,          ...  39  94 

manufacture  of  Iron  and  Steel, 40  96 

Plates,  drilled, 50  123 

punched, 5°  I23 

Portable  Boilers, 175  3°9 

Power  and  efficiency,  combined, 253  489 

of  Boilers 175  3^9 

Steam  Boilers,       .         . 144  291 

Precautions, 292  614 

Preservatives  and  Paints, 227  458 

Pressing  and  Flanging 189  402 

Pressure,  computation  of  Internal  Work  and,      ....  134  271 

excess  of, 221  454 

in  Boiler,  choice  of, *49  3O3 

steady  rise  of, 283  589 

Pressures,  control  of  Steam, •  2I5  449 

relations  of, 136  273 

Priming 2I9  45* 

Principles  of  Boiler-Design .150  304 

Problem  of  Boiler-Design,  details  of  the, 166  345 

Production  of  Heat,  methods  of, 9°  2o8 


668  INDEX. 

SEC.  PAGE 

Products  of  Combustion,  temperature  of,    .        .        .        .  78  179 

Pulverized  Fuel, 71  164 

Punching  and  Drilling,         ........  189  402 

Q 

Quality  of  Metal,  specifications  of 204  436 

Quantities  of  Heat,       .........  91  210 

R 

Rate  of  Combustion,  ........  79  184 

Records  for  Boiler-trials, 257  514 

Regnault's  researches  and  methods,  ......  140  280 

tables, 141  281 

Resilience,  ..........  29  56 

Riveting  and  riveting  machines, 191  404 

Rivet-iron  and  Steel,  rivets  and, 47  114 

Rivets  and  rivet-iron  and  Steel,  ......  47  114 

forms  of, 48  115 

Rivets,  sizes  of, 48  115 

strength  of, 48  115 

Riveting,  Steam  and  Hand, 5*  I25 

S 

Safety  Valves 183  385 

Sample  specifications, 203  421 

Scotch  Boilers, .         .         .         .  19  32 

Sea-water;  deposits  and  remedies,       .        .         .         .        .         .  123  256 

Seams:  fractured, 22O  453 

Helical, 49  JI7 

strength  of  riveted, 49  XI7 

Welded, 52  127 

Sectional  Boilers,          ....         sees.  20,  154,  197;    pp.  35,  3*4,  423 

and  Water- tube  Boilers 174  364 

Security  of  Boilers,  relative,         .......  284  592 

Sediment,              230  462 

and  Incrustation, 280  574 

Sensible  and  Latent  Heat,             112  243 

Setting,  contact  with, .  228  461 

Shapes,  "  Struck-up"  or  Pressed,          ......  53  127 

Shearing, 188  402 

Shell  and  Sectional  Boilers,  relative  strength  of,          .         .         .  58  148 

Shell  Boilers, , 154  314 

common  stationary,        ......  15  21 

Shells  of  Boilers,           .         . 55  129 


INDEX.  669 

SEC.  PAGE 

Size  of  Boiler,       .         .         .         .         .                  .         .         .         .  164  340 

Sizes  of  Tube,  standard, 165  341 

Solid  Fuels, .         .         .211  445 

Solids  defined • no  241 

Solution  of  Problems,  general  methods  of,           ....  26  43 

Spacing  of  Tubes,         ........  165  341 

Specific  Volumes  of  Steam  and  Water,          .....  135  272 

Specifications  and  contract,  purpose  of, 199  425 

generally,  form  of, 201  427 

Spheroidal  State, *         .         .130  268 

of  Water, 282  583 

Standard  Boilers,  Marine,             21  38 

Forms  of  Boiler,  development  of,         ....  2  2 

modern      .         .        .        .        .        .  12  20 

method,  instructions  and  Rules  for,      ....  256  491 

Stayed  and  Braced  Surfaces,         .         .         .         .         .         .         .60  151 

Staying  in  Boilers, 192  413 

Steam  alone,  energy  of, 270  548 

gauges,       .                                    185  393 

generation  and  application.        .         .         .         .         .         .119  252 

getting  up  of,      .         .         >         .         .         .         .         .         .  207  441 

stored  energy  in;  Tables,  .......  142  285 

superheating,      ...                  131  269 

quantity  of 259  517 

and  efficiency, 163  338 

and  Water  pipes, 182  383 

specific  Heats  of, 137  275 

volumes  of,          .        .                 .         .135  272 

Steam  Boilers,  Powers  of, 144  291 

Steam  Pressures,  control  of, 215  449 

Steel,  characteristics  of,                           31  63 

Steel,  choice  of,  for  various  parts, 44  112 

special  precautions  in  using, 46  113 

specification  of  quality  of,            ......  43  108 

Rivets  and  rivet-iron  and,           ......  47  114 

and  Iron  compared,            .......  38  92 

durability  of,        .......  225  457 

method  of  Test  of,       ......  41  98 

Stopping  suddenly, 219  9 

Stored  energy  in  Steam;  Tables, 142  285 

Strength  of  Metal,  loss  of, 59  149 

principles  relating  to,         ......  28  45 

Stress,  margin  of .         .  34  74 

Surfaces,  Stayed  and  Braced,       .         .         .         .         •        .         .60  151 


6/O  INDEX. 

T 

SEC.  PAGE 

Technical  uses  of  Water,      .        .        .        .        .        .        .        .124  260 

Temperature,  differences  of,         .         ......  290  609 

effects  of,                          ...         .         .         .36  83 

Heat  energy  as  related  to,     .....  102  235 

of  Fire,                    .         ......  76  172 

of  products  of  combustion,    .....  78  179 

Temperatures,      .         .         .         .         .         .....  91  210 

relations  of,    .                  .         .....  136  273 

Tenacity  .....         .......  29  56 

Test,  apparatus  and  Method  of,            ......  254  489 

of  Boilers,  inspection  and,           ......  56  140 

of  Iron  and  Steel,  method  of,      ......  41  98 

Tests  of  Metal,  specification  of,  .         .         .         .         .         .         .  204  436 

results  of,            .........  42  104 

Test-trials,  results  of,  .........  258  504 

Standard,    .         .         .......  255  491 

Theory  of  Calorimeters,       .         .......  261  521 

explosions,  Colburn's,          ......  275  559 

Theories  of  explosions,         ........  274  558 

Thermal  and  Thermodynamic  relation,       .....  132  270 

Thermodynamic  relation,  Thermal  and,       .         .         .         .         .  132  270 

Thermodynamics,         .         .         .         .         .         .         .         .         .116  245 

defined,    ........  106  238 

first  law  of,                .         .         .         .         .         .  107  239 

second  law  of,          ......  108  240 

application  of,    .         .                  .  117  247 

Thermometry,      ..........  92  214 

Time,  effect  of,     ..........  34  74 

Total  Heats,  computation  of,                 .                  .                  .         .  138  276 

Transfer  of  Heat,  efficiency  of,             .         .         .         .         .-..,-••  237  473 

Transportation  of  Boilers,   .         .         .         ...         .         .         .  198  424 

Tubes,  leaky,        ..........  220  453 

setting  of,                   .         .......  192  413 

standard  sizes  of,     .         .         .         .         .         .         .  .    .    .   .  165  341 

spacing  of,        .         .         .         .         .         .         .         .         .  165  341 

Tubular  Marine  Boilers,       .         .....         .         .  173  362 

Type  and  Location  of  Boiler,  selection  of,            .         .         .  147         .    300 

Types  of  Boilers,  mixed,      ........  13  20 

special  purposes  and  modern,           ...  4  7 


Upright  Boilers,  .      ~.         .        .        .        .        ^        .        .     175  369 


INDEX.  671 


PAGE 


Value  of  Boilers,  determination  of,      ......  246  485 

Valves,  deranged  safety, 221  454 

Vaporization, 131  269 

Latent  Heats  of  Fusion  and,  .         .        .        .        .114  244 

Variation  of  Form,  effect  of, 32  64 

Volumes,  relations  of, 136  273 

W 

Water  analysis, 125  261 

and  Steam  pipes, 182  383 

Specific  Heats  of,              137  275 

changes  of  Physical  states  of, 128  265 

composition  and  chemistry  of, 121  254 

de-aeration, 281  578 

low,  causes  of, 279  568 

consequences  of, 279  568 

Physical  characteristics  of,                  127  263 

properties  of;  Water  as  a  Solvent,   .....  120  253 

purification  of,           ........  126  262 

sources  and  purity  of  "  fresh," 122  255 

specific  Volumes  of  Steam  and, 135  272 

Spheroidal  State  of,            .......  282  583 

superheated, 130  268 

energy  stored  in, 281  578 

Technical  uses  of, 124  260 

Water-supply,  regulation  of,         .         .         .         .         .         .         .  216  449 

Water-tubes,          .                  153  314 

and  Sectional  Boilers,      ......  174  364 

Weather  waste  of  fuel, 82  191 

Weakness,  developed,  of  Boilers, 287  601 

Welded  Seams,     .         . .  52  127 

Welding,              * I9i  4O4 

Wood,           .                 68  159 

Work,  internal  pressure  and, 133  271 

Working  iron,  method  of 45  u3 


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Taking  Diagrams,  Computing  the  Horse  Power,  Drawing  the 
Theoretical  Curve,  Calculating  Steam  Consumption,  Determining 
Economy,  Locating  Derangement  of  Valves,  and  making  all  de- 
sired Deductions;  also,  Tables  required  in  making  the  necessary 
Computations,  and  an  Outline  of  Current  Practice  in  Testing 
Steam  Engines  and  Boilers.  By  Frank  F.  Hemenway,  Associate 
Editor  "  American  Machinist,"  Member  American  Society 
Mechanical  Engineers,  etc.  Second  edition,  1887.  12nio,  cloth.  200 

••  The  most  interesting  book  on  Steam  Engineering  that  we  have  ever  read." 
— National  Car  and  Locomotive  Builder. 

"Should  bo  in  the  hands  of  every  Engineer.1'— Engineering  News. 

"  Must  be  a  boon  to  the  every-day  Engineer  who  is  seeking  information.'1— 
Sanitary  Engineer. 

HERRICK.  QUANTITATIVE  ANALYSIS.  A  Translation  of  "Quanti- 
tative Chemische  Analvse  Durch  Electrolyse,"  of  Dr.  Alex.  Clas- 
sen. By  Prof.  Wm.  Hale  Herri ck.  Well  illustrated.  8vo 2  50 

"  The  work  is  the  standard,  and  the  only  source  of  information  in  English  for 
most  of  the  facts;  and  should  prove  indispensable,  not  only  in  teaching  electro- 
lytic methods,  and  in  laboratories  for  research,  but  in  many  technical  labora- 
tories, especially  those  connected  with  metallurgical  works." 

JOHNSON.          THE   THEORY   AND  PRACTICE  CF    SURVEYING. 

Designed  for  the  use  of  Surveyors  and  Engineers  generally,  but 
especially  for  the  use  of  Students  in  Engineering.  Second 
edition,  revised.  By  J.  B.  Johnson,  C.E.,  Prof,  of  Civil  Engin- 
eering, Washington  University,  etc.,  etc.  Illustrated  by  up- 
wards of  150  engravings,  with  folding  Maps,  Tables,  etc.,  etc. 
Third  edition,  thoroughly  corrected,  1887.  8vo,  cloth 3  50 

"On  the  whole  this  is  the  best  treatise  on  Surveying  that  we  know  off."— - 
Railroad  Gazette. 

•'  Whatever  branch,  of  work  the  Surveyor  is  in,  he  will  find  this  book  valuable 
and  exhaustive." — American  Engineer. 

KIDDER.  THE  ARCHITECT'S  AND  BUILDER'S  POCKET- 
BOOK  of  Mensuration,  Geometry,  Trigonometry,  Rules,  Tables, 
and  Formulas  relating  to  the  strength  and  stability  of  Founda- 
tions, Walls,  Buttresses,  Piers,  Arches,  Posts,  Ties,  Beams, 
Girders,  Trusses,  Floors,  Roofs,  etc.,  etc.  Statistics  and  Tafcles 
Relating  to  Carpentry,  Masonry,  Drainage,  Painting  and  Glazing, 
Plumbing,  Plastering,  Roofing,  Heating  and  Ventilation,  Weights 
of  Materials,  Capacity  and  Dimensions  of  Churches,  Theatres, 
Domes,  Towers,  Spires,  etc.,  etc.  By  F.  E.  Kidder,  C.E.,  Con- 
sulting Architect.  Upwards  of  600  p&ges  and  over  400  plates. 
Fourth  edition,  enlarged  (1887)  ...  3  50 

"  The  book  admirably  fulfills  its  purpose  of  becoming  an  indispensable  com- 
panion in  the  wori:  of  every  Architect,  young  or  old."— American  Architect. 


MERCUR 
& 

MAHAN. 

IV.ICHIE. 
PENCOYD. 


REED. 


RUSKIN. 


SEARLES. 


SINCLAIR. 


SMITH. 


TRAU  TWINE. 


PERMANENT  FORTIFICATIONS.    By  Prof.  D.  H.  Mahan. 
Kevisedand  brought  up  to  date  by  Col.  James  Mercur,  U.  S.  Mil- 
itary  Academy,  WestPoint.  Numerous  Plates,  1887.    8vo,  3^  mor.  $7  50 
"This  Work  is  a  Text-Book  in  the  U.  S.  Military  Academy,  West  Point." 

ELEMENTS  OF  ANALYTICAL  MECHANICS.    By  Col. 


Peter  S.  Michie,  ^?  U.  S.  Military  Academy.     8vo,  cloth,    1887..     3 
"  A  revised  edition,  as  taught  to  the  Cadets  of  U.  S.  Military  Academy,  West 


00 


Point. 

IRON    CO.'S    POCKET-BOOK    (THE).     Containing   many 
valuable  Tables  and  Calculations  of  interest  to  Bridge  Engineers 
and  Users  of  Iron  Beams  in  general,  together  with  the  Standard 
Shapes  and  Dimensions  of  this  Company.     Fourth  edition,  re- 
vised and  enlarged,  1887.     Containing  39  pages  of  Plates  giving 
Pencoyd  Shapes.     12mo,  morocco  flaps  .......................     2  50 

"To'Ensineers  ;md  Builders  in  Iron  and  Steel  this  volume  is  presented  with 
the  hope  that  it  may  be  of  assistance  to  them  in  their  daily  labors." 

TOPOGRAPHICAL    DRAWING    AND    SKETCHING. 

Including  Applications  of  Photography.  Illustrated  with  Plates, 
colored  and  plain.  By  Lt.  Henry  A.  Reed,  Ass't  Professor  of 
Drawing,  U.  S.  Military  Academy,  West  Point.  4to,  cloth  .  .  3  50 

"  This  is  decidedly  the  best  work  of  its  class  that  we  have  ever  met  with."  — 
Engineering  News. 

"An  expert  at  our  elbow  says  that  this  is  one  of  the  best,  works  on  tie  subject 
in  the  English  or  any  other  language."—  Engineering  and  Mining  Journal. 

"We  can  commend  without    reservation    Lt.    Reed's   work."—  Franklin 
Institute. 
THE    WORKS    OF    JOHN   RUSKIN. 

New  issue  of  the  12-  volume  edition,  1887. 
NEW  STYLES  OF  BINDING. 

12  Volumes,  containing  several  hundred  woodcuts,  some  of  them 
full  page.  Extra  brown  cloth.  ..........  .  ...  ..............  12  00 

12  Volumes,  with  all  the  woodcuts  and  206  full-page  Plates, 
colored  and  plain.  Extra  blue  cloth  ...................  .......  18  00 

12  Volumes,  with  all  the  woodcuts  and  Plates.     Fine  %  calf.  .  36  00 

FIELD  ENGINEERING.  A  HANDBOOK  of  the  Theory  and 
Practice  of  RAILWAY  SURVEYING,  LOCATION,  and  CONSTRUC- 
TION, designed  for  CLASS-ROOM,  FIELD,  and  OFFICE  USE, 
and  containing  a  large  number  of  Useful  Tables,  Original  and  Se- 
lected. By  Wm.  H.  Searles,  C.E.,  late  Prof,  of  Geodesy  at  Rens- 
selaer  Polytechnic  Inst.,Troy.  This  volume  contains  many  short  and 
unique  methods  of  Laying  Out,  Locating,  and  Constructing  Com- 
pound Curves,  Side  Tracks,  and  Railroad  Lines  generally.  It  is 
also  intended  as  a  Text-Book  for  Scientific  Schools.  Pocket-book 
form.  Eighth  edition,  with  additions,  1887.  12mo,  morocco  ...  3  00 

"I  have  made  an  examination  of  '  Field  Engineering  '  by  W.  H.  Searles,  C.E. 
The  book  i*  admirable.  The  internal  arrangements  and  appearance  are  excellent. 
It  is  an  easy  work  to  refer  to  and  isplainand  clear.  There  is  no  useless  lumber 
in  it.  Every  sentence  belongs  there."—  Prof.  Davis,  University  of  Michigan. 

LOCOMOTIVE-ENGINE  RUNNING  AND  MANAGE- 
MENT. A  Practical  Treatise  on  the  Locomotive  Engines, 
showing  their  performance  in  running  different  kinds  of  trains 
with  economy  and  dispatch.  Also,  directions  regarding  the  care, 
management,  and  repairs  of  Locomotives  and  all  their  connec- 
tions. Illustrated  by  numerous  engravings.  8th  edition,  1887. 
12mo,  cloth  ........  *  .............  ............................  2  00 

"It  is  a  very  comprehensive  and  thoroughly  practical  work."  —  American 
Machinist. 

"The  more  it  is  studied,  the  more  thoroughly  will  it  be  appreciated."— 
National  Car  Builder. 

'•  The  book  only  needs  to  be  known  to  have  a  wide  sale."  —  Railway  News. 

A  TREATISE  UPON  CABLE  OR  ROPE  TRACTION, 

as  applied  to  the  working  of  STREET  and  other  RAILWAYS. 
(Revised  and  Enlarged  from  Engineering.)  By  J.  Bucknall  Smith, 
C.E.  With  illustrations  and  folding  Plates.  4to,  cloth  ........  3  50 

"  The  publication  of  this  book  seems  to  us  to  be  most  timely.  The  subject  is 
ably  handled  by  an  experienced  Engineer."  —  American  Machinist 
CIVIL  ENGINEER'S  POCKET-BOOK  of  Mensuration, 
Trigonometry,  Surveying,  Hydraulics,  Hydrostatics,  Instruments 
and  their  Adjustments,  Strength  of  Materials,  Masonry,  Princi- 
ples of  Wooden  and  Iron  Roof  and  Bridge  Trusses,  Stone  Bridges 
and  Culverts,  Trestles,  Pillars,  Suspension  Bridges,  Dams,  Rail- 
roads, Turnouts,  Turning  Platforms,  Water  Stations,  Cost  of 
Earthwork,  Foundations,  Retaining  Walls,  etc.  In  addition  to 
which  the  elucidation  of  certain  important  Principles  of  Con- 
struction is  made  in  a  more  simple  manner  than  heretofore.  By 
J.  C.  Trautwine,  C.E.  12mo,  morocco,  flaps,  gilt  edges.  28th 
thousand,  revised  and  enlarged,  with  new  illustrations,  by  J.  C. 
Trautwine,  Jr.,  C.E.  (1887.).  .  -  ....................  5  00 

"It  is  the  best  Civil  Engineers'  Pocket-Book  in  existence."—  American 
Engineer. 


TRAUTWINE. 


WADDELL. 


A  METHOD  OP  CALCULATING  THE  CUBIC  CON- 
TENTS  OF  EXCAVATIONS  AND  EMBANKMENTS 
BY  THE  AID  OP  DIAGRAMS,  together  with  Directions 
for  Estimating  the  Cost  of  Earthwork  By  John  C.  Trautwine, 
C.E.  Ninth  edition,  revised  and  enlarged  by  John  C.  Traut- 
wine, Jr.,  1887.  8vo,  cloth $2  00 

THE  PIELD  PRACTICE  OP  LAYING  OUT  CIRCU- 
LAR CURVES  POR  RAILROADS.  By  J.  C.  Trautwine, 
Civil  Engineer.  12th  edition,  revised  by  J.  C.  Trautwine,  Jr., 
1887.  12mo,  limp  morocco , 


2  50 


"  Probably  the  most  complete  and  perfect  treatise  on  the  sinirle  subject  of  Rail- 
road Curves  that  is  published  in  the  English  language."— J~ 


-Engineering  News. 


THE  DESIGNING  OP  ORDINARY  IROiv  HIGHWAY 
BRIDGES.  A  new  Practical  Work,  with  many  Tables  and 
Illustrations.  Third  editibn.  With  an  additional  Plate,  etc.  By 
J.  A.  L.  Waddell,  Member  of  the  Society  of  Engineers,  and  Pro- 
fessor in  the  University  of  Tokio,  Japan.  8vo,  cloth 4  00 


"His  book  is  probably  the  most  valuable  contribution  to  the  literature  of 
Iron  Bridge  building  that  has  yet  appeared."— American  Engineer. 

"  We  strongly  recommend  the  book  to  Students  and  Engineers  desirous  of 
learning  the  art  of  Bridge  design."— Engineering  News. 

'•  The  book  will  be  found  of  the  greatest  value  to  County  Commissioners,  and 
all  others  who  have  to  make  contracts  with  Builders  of  Iron  Highway  Bridges, 
etc.,  etc." — Railway  Age. 

WARREN.  A  PRIMARY  GEOMETRY.  With  simple  and  practical  ex- 
amples in  Plane  and  Protective  Drawing,  and  suited  to  all  begin- 
ners. By  S.  Edward  Warren,  C.E.,  late  Professor  in  the 
Rensselaer  Polytechnic  Institute,  Troy,  N.  Y.,  etc.,  etc.  12mo, 
cloth 75 

"•  The  object  of  this  volume  is  to  contribute  to  a  general  earlier  beginning  of 
the  study  of  Geometry;  in  the  belief,  moreover,  that  without  such  a  beginning, 
elementary  education  is  somewhat  one  sided. 

"It  is  expressly  adapted  to  '  MANUAL  TRAINING.'  " 

GENERAL  PROBLEMS  IN  THE  LINEAR  PERSPEC 

TIVE   OP   FORM,    SHADOW,   AND  REFLECTION. 
OR     THE     SCENOGRAPHIC     PROJECTIONS    OP 
DESCRIPTIVE  GEOM1ETRY.  '  By  Prof.  S.  Edward  War- 
ren,  C.E.     New  edition,  revised,  1887.     17  folding  Plates.     8vo, 
cloth 3  50 

"  In  use  as  a  Text-Book  in  the  Rensselaer  Polytechnic  Institute,  Troy,  N.  Y., 
etc.,  etc. 

WELLINGTON.  THE  ECONOMIC  THEORY  OP  THE  LOCATION  OP 
RAILWAYS.  An  Analysis  of  the  Conditions  controlling  the 
laying  out  of  Railways  to  effect  the  most  judicious  expenditure  of 
capital.  By  Arthur  M.  Wellington,  Chief  Engineer  of  the  Vera 
Cruz  and  Mexico  Railway,  etc.  New  and  improved  edition.  8vo,  5  00 

"  Mr.  Wellington  has  done  great  service  to  the  Railroad  profession  ;  more 
particularly  to  Engineers,  Managers,  and  Superintendents,  by  bringing  together 
in  a  single  volume  such  a  mass  of  valuable  matter.  It,  should  be  in  every  Rail- 
way Library.1'— Railway  Age. 

WEST.  AMERICAN  FOUNDRY  PRACTICE.  Treating  of  Loam, 
Dry  Sand,  and  Green  Sand  Moulding,  and  Containing  a  Practical 
Treatise  upon  the  Management  of  Cupolas,  and  the  Melting  of 
Iron.  By  Thomas  D.  West,  Practical  Iron  Moulder  and  Foundry 
Foreman.  Fully  illustrated.  Sixth  edition,  1887,  revised  through- 
out. 12mo,  cloth. 250 

"  We  can  commend  the  book  as  the  best  we  know  off  in  its  special  line."— 
Sanitary  Engineer. 

"Every  possible  disaster  that  can  be  suggested  by  a  long  training  is  set  forth 
with  its  cause  and  the  method  by  which  it  can  be  avoided. "—Engineering 
(London}. 


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